I'd like to add a point of caution here: as with many privileges, it's important to make sure you don't give people access to them too early.

A silver tag badge is easier to gain than you might think, and doesn't necessarily require a wide knowledge of the subject area. There's at least one case of a user having >400 (as of the time of writing, 574) net upvotes and >80 (as of the time of writing, 91) non-community-wiki answers on a single question. As such, any tags placed on that question will automatically give the user in question the corresponding silver tag badge (assuming that the tag itself is eligible for tag badges). I don't think answers to a single question, impressive though they are (they got those 400 upvotes for a reason), can demonstrate much about the knowledge of the tag more generally (the user will probably be an expert in one of the tags in question, but the others might well be incidental).

I'm finding it hard to think of a privilege which is cosmetic enough that it could safely be awarded in this sort of situation. (Of course, we could treat this similarly to brand new users who got moderation tools as a consequence of claiming a bounty, but those users tend not to be able to use the tools correctly either; I know that I ended up misusing moderation tools quite a bit early on due to gaining the reputation for them before I really understood how the site worked.)

I'd like to add a point of caution here: as with many privileges, it's important to make sure you don't give people access to them too early.

A silver tag badge is easier to gain than you might think, and doesn't necessarily require a wide knowledge of the subject area. There's at least one case of a user having >400 (as of the time of writing, 574) net upvotes and >80 (as of the time of writing, 91) non-community-wiki answers on a single question. As such, any tags placed on that question will automatically give the user in question the corresponding silver tag badge (assuming that the tag itself is eligible for tag badges). I don't think answers to a single question, impressive though they are (they got those 574 upvotes for a reason), can demonstrate much about the knowledge of the tag more generally (the user will probably be an expert in one of the tags in question, but the others might well be incidental).

I'm finding it hard to think of a privilege which is cosmetic enough that it could safely be awarded in this sort of situation. (Of course, we could treat this similarly to brand new users who got moderation tools as a consequence of claiming a bounty, but those users tend not to be able to use the tools correctly either; I know that I ended up misusing moderation tools quite a bit early on due to gaining the reputation for them before I really understood how the site worked.)