e-mails having attachment don't have a sign next to it in the mail list.
when opened, you still can't see the attachments existence. swiping the mail body from right to left doesn't help.
i'm using android 2.3.3 on samsung i9000. gmail. a few has wrote the same complain on google playstore.
edit: somehow, one attachment is visible. i had sent that mail from my mail.com account from my phone to check the problem.