I've opened up some TIFF graphics in Photoshop CS4. When going to
Image -> Mode, they all show "Grayscale" and "8 bits per channel" checked. But when looking at the tabs, some show "Gray/8", and others show "Gray/8#". What's the difference?
"If ... you see a pound sign (number sign, #), it means your image has no color profile associated with it." From Earthbound Light, "What Do Those Symbols after the File Name Mean in Photoshop's Title Bar?"
That's the best I could find. I know you're not asking about the title bar, but it seems likely related.
Essentially, this short piece explains the logic behind the pattern you describe (slash, number, symbol), so it should be applicable here. It boils down to this:
Grayscale/8 = grayscale with 8-bit depth in the working color profile
Grayscale/8* = grayscale with 8-bit depth and color profile mismatch
Grayscale/8# = grayscale with 8-bit depth but no associated color profile