We have not worked out any policy on this, but I always assumed we would only assign issues to people with commit privileges. I quick check suggests that you don't have them, Jesus. We can give you the rights to modify issues and set the assignment, but I don't know if you should be able to be assigned a bug yet.
What do other people think?
That has exactly been the policy that I have been executing, yes. As for giving additional rights on a per-user basis - that's tricky to implement. We have the User and Developer roles in the tracker, and you get additional rights only with additional roles, normally. I also agree with Nick as to what the purpose of assignments is. To indicate that you are working on a specific issue, a message saying so is enough (which could also include estimated completion dates, which a mere self-assignment can't). Regards, Martin