I lamented the poor quality of the photo and asked for clarification.
Since then, Joseph Lauer has drawn my attention to a blog post by Bryan Windle which includes much better photos of the object. Bryan also links to an article by Zvi Koenigberg in the Jerusalem Report (Jerusalem Post) which gives a more detailed account of the amulet.
If am reading Koenigberg correctly, the inscription on the amulet is on the inside and is only visible on the computer 3-D model which reconstructs the view of the outside and inside. Until we see that reconstruction, it is difficult to evaluate the claim.
I see no clear indication of deliberate markings on the new photo of the still unopened amulet. But they would be visible, if at all, only as an external indentation of marks that are on the inside. So for now I withhold judgment on the claim.
If you want to know what to look for, look at the drawing of the Izbet Sarta abecedary by Frank Moore Cross in this Bible History Daily post. You may need to expand the drawing for a clear view. The Izbet Sarta inscription contains multiple copies of the Canaanite alphabet from around the same time period as the altar on Mount Ebal.
Look on the far left side of the first and last lines. That letter is an aleph. It was originally a drawing of an "ox" head (aleph means "ox" in Canaanite/Hebrew). The stance of the letter varies, but it looks a bit like a rounded capital letter "A" lying on its side. Turn the "A" until it is upside down and you can see the stylized head with the two horns sticking out.
That is what I would expect to see on the inside of the Mount Ebal amulet if there is a letter aleph there. Again, I await more information.
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