Rajaram (who takes sole responsibility for writing the book) explains his view of the seals on p. 162:

The 'horse seal' goes to show that the oft repeated claim of "No horse at Harappa" is entirely baseless. Horse bones have been found at all levels at Harappan sites. Also, as we have already seen, the word 'asva' is a commonly occuring [sic] word on the seals. The supposed 'horselessness' of the Harappans is a dogma that has been exploded by evidence. But like its cousin the Aryan invasion, it persists for reasons having little to do with evidence or scholarship. A well known 'Dravidianist' [I. Mahadevan] tried to argue with Rajaram that the animal on the seal in question (Mackay 453) is not a horse but a unicorn bull. A comparison of the two creatures, especially in genital area shows this to be fallacious.

(Addendum added 30 July 2000: An email from Rajaram today revealed that his image was, in fact, a "computer enhancement" produced to facilitate his reading. Significantly, this was not mentioned in his book. I earlier suggested on the Indology List that the image was artificially manipulated to manufacture his "horse" from a broken seal.)

Second, when I spent many hours looking through the only book that Rajaram references in his study to Mackay (on p. 262), I couldn't find the seal. That made me even more suspicious. Given the importance of Rajaram's supposed discovery, you'd certainly expect the source of that find to be given correctly in his bibliography!

I consequently spent several days studying every book and article of Mackay's that I could get my hands on. I also emailed Rajaram and asked for the reference. (He didn't respond until after I posted my findings on the Indology List.) I eventually found Mackay 453 in Plate XCV of Vol. II of Further Excavations of Mohenjo-Daro (New Delhi, 1938).

The picture in Mackay is tiny and not very clear, but it is a lot clearer than it is represented as being in Rajaram's book. Here - but not in Rajaram's book - you can clearly see that the seal is damaged. Indeed, the whole of the neck and head of the unicorn bull is broken off. And the "head" and "neck" in Rajaram's reproduction disappear when you look at the original. The "head" and "neck" are made up of a crack and part of the inscription in the original, seen below:

In the photo we see no genitals, which in unicorn bull seals normally show up about where the heavy shadow and crack are in Mackay 453. Rajaram uses this as "evidence" that here we have a horse. But Professor Witzel has located another unicorn bull seal with exactly the same inscription in Asko Parpola et al., eds., A Corpus of Indus Seals and Inscriptions, Vol. II: Collections in Pakistan (Helsinki 1991, p. 63, seals M-772 A) that also does not show any genitals (which are easily damaged and don't always show up in the seals).

Below is the seal that Witzel found, compared with Rajaram's supposed horse seal. (Note that M-772 A is apparently a seal and not a seal impression, like Mackay 453, so the original image in Parpola is reversed. I've flipped it horizontally in the image below to make comparison of the identical inscriptions easier. M-772 is clearer than my scanned image of Mackay 453 because Parpola's photographs are vastly superior to Mackay's):

The fact that both animals are the same is made obvious by the fact that the inscriptions are identical. Note also that the tails are the typical "rope" tails normally associated with unicorn bull seals found at Mohenjo-daro. The rope-like nature of 453 is even clearer in Mackay's original picture. It is adamantly not a "bushy tail," as claimed by Rajaram in a recent email message quoted at the end of this webpage (although Rajaram's story is certainly a "bushy tale"!).

One of the most amusing parts of the story comes in the fact that an extant seal impression made by M-772 does show part of the missing genitals (there also seems to be some damage in the seal at that point) - found exactly where we expect them. Here is the relevant image from Parpola (again, courtesy of M. Witzel). Note again the identical inscription:

Because of the lighting in this photograph, the "rope" tail of the unicorn bull in this seal impression might look a little smudged or "bushy." Study of the seal itself (M-772 A, shown earlier) shows that this is purely an artefact of the reproduction.

Finally, I'll add an image of a fuller unicorn bull for reference purposes (found on the same page of Parpola as M-772 A (the seal) and M-772 a (its impression). The inscription in this case is obviously different. Note again the "rope" tail:

Conclusions:
 

1. Rajaram's horse is bull (unicorn bull, that is).

2. The distorted image of Mackay 453 shown in his book hides that fact. You can't even tell in Rajaram/Jha that Mackay 453 is severely damaged! It is only because the image is distorted - with a "head" and "neck" arising out of the blurred image of the crack and part of the inscription - that the "Artist's reproduction" isn't immediately seen to be pure fantasy.

3. Rajaram's misreference in his book to the source of Mackay 453 makes it very difficult for anyone to track down the original cracked seal.

4. My offer (made last week in Indology) stands that I will give $1000 to anyone who convinces a single reputable IVC expert recognized in the West that Rajaram's hoax is a "horse seal."
 

...if you insist that the animal with a bushy tail is still a bull, you are entitled to your beliefs. If this is your  attitude - refusing to see the evidence of not only the seal and the horse bones that have been known since 1935 - I see little point in continuing the dialog. Let us leave it that (27 July 2000).

The problem seems to be that many Indologists are still trying to work within the framework of nineteenth century formulation. When new evidence came to light, especially in the past 60 years, instead of reexamining their formulations, they are trying to select, discard and manipulate dat[a] to preserve their beliefs. This bespeaks a t[h]eological rather than a scientific mindset. A debate with such people is pointless (21 July 2000).