There should be some way (e.g. a special page accessible from the user page,
or a marking on the user page itself) to display the rights of a specified user.
Now, AFAIK the only way is to look through Special:Listadmins for the user and
look whether he is sysop or not. (Or, theoretically, look through Special:Listusers...)
Alternatively, the user/admin list could be made searchable, but that is IMHO a worse idea.