Sometimes, hotel staff, concierges, travel guides, or other people have provided special service when we travel.
For instance, the concierge who moved us to a different room...on the concierge level. Our original room was right next door to some people with some noisy puppies. Cute...but noisy. We didn't have concierge status at that hotel, but he was making up for our noisy neighbors.
Then there was the server at a restaurant who brought us the chef to explain his recipe when I asked her to compliment the chef on the dessert.
These and other special treatments are part of their job...and much more. Sometimes a simple thank you is not enough. A fellow traveler takes a small pack of decorative post cards with her when she travels and writes a thank you before she leaves. Then she gives the thank you to the person the next day, or after the meal, or a little later. It's unexpected and a nice gesture. And, it looks better than using the hotel stationery!