I need a bit of help.
How do you think Snape contacted members of the Order in OOTP? I'm thinking specifically
about him checking that Sirius wasn't at The Ministry and also when he contacted them to say that Harry and the others were in danger.
He couldn't use the Floo Network and I don't think he used his Patronus because no one seems to know that his Patronus is a doe. (unless he changes his Patronus for order work!)
I was thinking about an owl but that's not very quick. Or possibly something like Hermione's charmed Galleons but I can't figure out what.