There are only few mechanical keyboards by IBM:
Huge and heavy ancient stuff which can't be confused with anything PC.
Model F XT and AT.
122 key Model F and M.
101 key Model M and variants (different colors, trackpoints, non-IBM branding, ...).
Space saving Model M (looks like normal M, but tenkeyless).
Model M2 - the most "modern" looking of all, for some values of "modern".
Model M15 - split M2.
Note: Ms and M2s exist in rubber dome versions as well, these can only be distinguished by product numbers or physical inspection.
