Thanks Qie for your reply, yes I think you understand the problem. But I am hoping to use in-world mechanisms only (no outside server interaction).
It would be good if someone can help figure out some kind of ingenious way of clicking on buttons without revealing to the clear which button was clicked.
The problem with textured letter prims (a,b,c,d) is that the texture uuid needs to be mapped to a buttonID which can be worked out if captured in transit. Also a sort of circular roller or object with indented mesh faces have the same problem.