It normally means the user has problems on provisioning some accounts. For instance suppose your user has 3 resources: AD, Ldap and Domino. If IDM had problems on creatint/updating its AD account then it flags with a triangle.
Sometime yellow tringle also comes when you provisioned/update any resouce to the user. Then in find user page we see yellow tringle (which means update needed).
To remove this yellow tringle just edit and save user with or without( if any update not needed). This is my practical exp.
Thanks for the help guys. As mentioned by Jay you update the account to clear this. I usually do this using Activesync and the update user workflow and any problems with any resources are removed. Would be more helpful if there was a way to find out exactly which resource caused this and why.
May not be practical but using /debug to look at the XML user data of the user, should give you a clear indication. Usually, the data that wasn't provisioned is persisted there for later try.
Also, you may have access to some reports trough Auditlog to help you figure out what went wrong.
Finally, you could update all the users in that org by selecting the org and choosing update but that's not that good of a practice!