If you don't know the txid you could scan the blockchain for new txIDs and use getrawtransaction on each of them to figure out if any outputs were sent to the multi-sig address.
Haven't implemented it yet so I'm not sure if it will work like this but so far it looks like it could imho.
Ok, so it turns out that you are right - it *is* possible to tell if someone has sent coins to a multi-sig address. This is the process:
* Start from last processed block hash
* Call getblock
* Iterate through all transaction ids (which really are *all* txids, and not just those in your wallet - this is the first part of the key to the process)
{
* call getrawtransaction on each txid (which also lets you inspect non-wallet transactions, 2nd part of the key to the process)
* Iterate through all vouts
{
* check each address in the scriptPubKey list to see if it matches your multi-sig address
* if it does, you've found a deposit! You can determine the number of confirmations from the call you made to getrawtransaction
}
}
* Goto next block hash
This is huge, because it means you can give out multi-sig addresses to your users and actually be able to credit them when the coins arrive!
Cheers, Paul.