The only time that admin should be allowed to use admin powers with out the tag is when coming in and catching a toggle hax.....
Then far as other admins that dont have a tag on i ask them if they are acting as senoir admin.....
Cause ill join again after playing another server and forget to put it on. But siimple general rule:

No tag = No powers.

And even if they don't have the tag on you shouldn't ban or mute them or anything ON Purpose. I emphasize that cause i can see admins doing that to another admin they dont like