Try 'validateaddress'. If you have the privkey in your wallet you will see sth like:
protoshared validateaddress PpgAhkokKXLXtdGq5jGNiYoHpLRowwR2dy
{
"isvalid" : true,
"address" : "PpgAhkokKXLXtdGq5jGNiYoHpLRowwR2dy",
"ismine" : true,
"isscript" : false,
"pubkey" : "03602a2ba62a5021a8d89afb03ce1b2a8fa2a353445c956333d532ba066553c1dc",
"iscompressed" : true,
"account" : ""
}
The important part:
"ismine" : true,