or just the "tMP" part of the (old) moderator avatar? But that avatar is already so old, that I don't really know any more who made these... I think it was Di? I'll have to look around in the moderator archive ;-) (as you see, I'm still wearing my christmas hat )
The characters tMP with treble clef seems fine to me - to, if wanted, make it more square the characters could be placed in a column and the clef moved to one side - but otherwise perhaps something based on the side view outline of a (three) piston valve block would be good. Just Music's web site uses valve buttons as icons for choices on its site, there might be some conflict but three buttons with the letters tMP above them is another possibility?