+ sometimes mainly means a medic cross
It is sometimes found on a nurse's nurse_cap.
8chan + drawme website = 8chan_drawings.
Trivia 
Edit
It could also mean "I read this and liked it", list example:
+ http://archive.4plebs.org/pol/thread/40093859/#40094237 + http://archive.4plebs.org/pol/thread/40189718 + http://archive.4plebs.org/pol/thread/40202033 + http://archive.4plebs.org/pol/thread/40572367 + http://archive.4plebs.org/pol/thread/40630337/ + http://boards.4chan.org/pol/thread/40721499 http://archive.4plebs.org/pol/thread/40083040 http://archive.4plebs.org/pol/thread/40093859 http://archive.4plebs.org/pol/thread/40093859/#40094909 http://archive.4plebs.org/pol/thread/40095995 http://archive.4plebs.org/pol/thread/40095995/#40105237 http://archive.4plebs.org/pol/thread/40164975 http://archive.4plebs.org/pol/thread/40164975 http://archive.4plebs.org/pol/thread/40208421 http://archive.4plebs.org/pol/thread/40286995 http://archive.4plebs.org/pol/thread/40299062 http://archive.4plebs.org/pol/thread/40407468 http://archive.4plebs.org/pol/thread/40431808 http://archive.4plebs.org/pol/thread/40469746 http://archive.4plebs.org/pol/thread/40470267 http://archive.4plebs.org/pol/thread/40488358 http://archive.4plebs.org/pol/thread/40559030 http://archive.4plebs.org/pol/thread/40584016 http://archive.4plebs.org/pol/thread/40630337 http://archive.4plebs.org/pol/thread/40640988
