I thought I would make the suggestion here after seeing a post in the discussion forum:
https://bitcointalk.org/index.php?topic=37892.0Basically, it would be great if the bitcoin client makes it easy for a user to append a "satoshi code" to a transaction. The extra amount will just be a 1-1000 satoshis, which is next to nothing in Today's value. These can be used for identification purposes. For example, if Meze Grill might ask their customer to include the order number in the transaction to help keep track of which order was paid. So if you ordered 2.03 btc worth a food, you might send them 2.03000087 btc for order #87.
The "satoshi code" can be added to either the output amount or the fee amount. I think the fee amount makes more sense, because it won't benefit the merchant (no matter how little) and it also won't screw up their accounting. And you can still send payments down to the satoshi amount with a transaction fee of 0.00500087.
I'm sure there are all sorts of other reasons that you may want to identify a transaction. And obviously if you want to use "satoshi codes" to convey your own personal message, you can to. What do you guys think?
First: bitcoin will never be used for point-of-sale transactions. It requires a minimum of 30 minutes - 1 hour (depending on the vendor's level of paranoia) to verify transactions and such a payment delay will never work in a point-of-sale setting. Lots of people propose ideas to try to get around this but they all require vendors to accept unvalidated transactions, which is equivalent to taking someone's word that they will pay, and if they're going to accept that level of trust (which no vendor will), then they might as well not request that you issue any kind of transaction at all at the point of sale and just allow you to leave with the promise to submit a transaction to the network at your convenience later.
Second: if a vendor ever were foolish enough to accept bitcoin at point-of-sale, and if they stayed in business long enough with all of the free goods they will end up giving out as a result, then I would expect that the easiest thing would be for the customer to submit a transaction to the vendor for the vendor to validate and then submit to the network on the customer's behalf. This customer-vendor exchange would be enough to establish that the payment was from the customer for the specific service or good being paid for, and there would be no need for tags within the transaction itself.