Hey @manfredkarrer, thanks for reaching out!
As discussed on the thread over at the Bitsquare forum, SBD is already taken.
I suggest SteemUSD, that is unlikely to change. To make it even clearer, it could be SteemUSD (Steem Dollars).
But if that is too long, I would go with SteemUSD - personal preference.
p.s: following you here on steemit now.