Or drop in or post a thank-you card or letter. Even if you don't know which station the crew in question are from, if you send it in to the relevant ambulance service HQ with enough details to identify them (date, approximate time and location of the incident) it will filter through to them. Every ambulance trust that I've been involved with has treated "thank you" messages as very important, and my current service publishes a list every month of crews who have had one, as well as sending each person involved a copy of the letter or card. Please do it. It doesn't happen often, and I don't know of anyone who doesn't like to get the occasional one.