I haven't been able to go through my Tolimas with enough piece of mind.
I did find one fake, unfortunately. On the 5c Brown from 1871:
I don't have any genuine of this stamp (wink wink), but I found one online that looks like one (credits to HowlingPixel.com):
The easiest clue to follow are the circles between the upper and lower inscriptions ("EE.UU. de Colombia" and "E.S. Del Tolima"). They look like a star (*) in these fakes. In the genuine stamps, they look like two concentric circles, the inner one being a solid circle, the outer being just a circumference. However, in the images of the genuine copies present in Dieter Bortfeld's book (The Workbook, Vol II, p207-211) the outer circles are joined to the inner ones in different zones and at different degrees depending on the position in the sheet so sometimes they look like one bigger solid circle.
They never look like a star though, like in this fake.