TextExpander version 6.5/2.0/1.0 introduces visual bubbles and visual blocks of text within the editor. Now your snippets will expand percent signs.
When it comes to TextExpander 6.2.8 and 1.0:
The percentage sign (%) is a special macro character in TextExpander snippets. It is used to indicate that date, time, or other information should be substituted at that point in your snippet.
To get a % to expand, just put %% in your snippet.
For example, if you want your snippet text to be “50% discount”, enter it as “50%% discount”.