That’s an interesting question. We can probably improve the IFTTT notification to carry the device name so that you can distinguish between the different messages. In the mean time, I think one work-around you can use is to apply for three IFTTT accounts, one for each of the OPenSprinkler, and for each IFTTT setup you can customize the message so that you can tell which controller it’s sent from. The reason you need three IFTTT accounts is that each account gives you only one Maker key.
In the future, as I said, we should probably include the device name in the message; or alternatively, support custom ‘event’ names, so that you can associate each event name with a different controller.