i dont do the social media thing, i dont think withthelove (who hosted the last several oga jams, i'm just filling in) had an official hashtag for the oga jam....
i suppose you could just do
#OpenGameArt
or
#OpenGameArtJam
to be totally honest, i don't even know exactly what hashtags are or what they do. the only "social media" i use is discord and the OGA forum