The .message-signature class has nothing to do with those fields.
I suspect you must have some other code somewhere which displays them.
Something like this should work, but you will likely need to increase the cell sizes or there will be wrapping to a new line.
You are right, signatures have nothing to do with this. I have just upgraded from 1.5.x and been working on my forum for xx hours now and am a bit tired.
Code for displaying info on my forum on mobiles is: