If you wanted to know if a particular mountain was formed by movement along a fault, what would you look for

If the mountain was in the Front Ranges of the Rockies, I would look for a thrust fault underlying the mountain since thrusting is a low angle fault which juxtaposes older rocks on top of younger and thickens up the stratigraphic sequence. Also, mountains can form from normal faults whereby the hangingwall of the fault  or the side of the fault which is towards the inclination of the fault drops down relative to the footwall (the side under the fault) so I would also look for a normal fault bounding a cliff face of the mountain.,

The answer would be abrasion.