UPDATE: it has been pointed out to me that the answer to this problem has been posted here in the context of re-numbering of tables.
A (not very exhaustive) search on "figure numbers" did not reveal a previous question about my problem, so here it goes:
Is there a way to add a prefix (say, a single letter) before the figure number in the figure caption?
Background: I want to create a supplementary data file in which the figures (say, Fig. S1, Fig. S2, etc.) appear differently from those in the main file (where they are called Fig. 1, Fig. 2, etc., as usual).
Is there a command, counter, or script available for this? Thanks in advance.