There's a question mark in front of the email addresses in Photo Stream
Photo Stream - Why is there a question mark in front of the email addresses of people I'm sharing photo's with?
iMac, Mac OS X (10.7.4), 2.0 Mhz
Question marked as
Best reply
The question mark indicates that the recipient has recieved the invitation and has not yet responded to it. Once the recipient accepts the invitation a tick mark would appear next to their email.