We have testnet addresses starting with m, but there is no bitcoin address starting with d or s.
Public keys on the other hand can start with those characters or even others but the facts is only very old wallets use public keys to receive Bitcoin.
Even public keys don't start with the characters mentioned by OP.
Public keys start with 02 or 03, if they are compressed and 04, if they are uncompressed.
I found these addresses in LoyceV's dumps, for Bitcoin. Seems like they are real.