So I've re watched the first two seasons of Game of Thrones and I can't find a single scene in which Stannis wears a crown. This lead me to wonder if he even has one. If he doesn't why doesn't he? If he does please include a picture or even a description from the books.
From GoT wiki:
The TV series has curiously not chosen to show many of the rival kings during the war wearing crowns. Joffrey and even Renly had crowns, but Robb, Stannis, and Balon have never been shown with their crowns. In the novels, Stannis has a new crown made resembling a circle of metal flames around his head, in honor of the Lord of Light (...)
This is from the page about last episode of season 3. Perhaps he has a crown in the 4th season, but I wasn't able to find any confirmation of this and I don't recall ever seeing him in a crown.