Noone gets tagged for having an alt account. Tags come into play when users enroll their alt accounts in the same campaign. Essentially cheating a signature campaign, twitter,  and sometimes bounty campaigns.

You also have to read the rules of a campaign. Most bounties may not care if you use multiple accounts. Long as the rules say it's ok, you should be good to go.

It's totally legal to have alt accounts, even some staff have alt accounts. Just don't abuse the system with them. Don't start conversations back and forth in a thread between your accounts. Don't merit your accounts.