I have been mulling over something similar for some time, I have an example of a signature on one piece that I have seen elsewhere on a few items and I think they are suspect. I have been told that they are kosher and that Harris changed his signature format for a short period but I still have my doubts. Actually, I think they are faked.
His signature could vary a little, no surprise really. To judge I look for one made with a diamond point engraver, the expected format and usually beautifully engraved well formed characters. The signatures are found on items that were very well executed, those signatures that I suspect I have seen on items that I was surprised to find signed - they all lacked a little in some way or another.
John