There may be an easy way to do this:
Doing some very large photo montages and I would like to put a number on each still in timeline order in order to help with the review process.
Then I'd like to remove those numbers several days later of course.
Do you want the number to show up in the preview window, or do you just want the number to show up somewhere on the timeline, for instance in a marker or region? There are lots of scripts that do the latter (e.g., assign a marker or region to every event and the number the marker or region).