You're a name I never expected to see again, lol
One of the most old school people I know. But yes, [SG] Is our tag for admins only, and has been since I believe at least 2009. I could be wrong on the year there, but it has been for quite some time.
I appreciate the fact that you were a admin and a well known member of SG for years, but even so, I'm afraid you cannot wear the tag unless you receive your admin back.
As far as the Member tag, or in your case, it would be the Supporter or regular tag, those are optional, and where they are not officially enforced anymore, they were at a point.
I do hope you stick around. If I remember correctly, your posts always made me laugh