Pirates of the Burning Sea is all for the user content submissions and it just happens that flag and sail submissions have been reopened. That's right, you can craft flags and sails of your own with the help of a dedicated forum. Then, after getting that perfect design it can be submitted for developer approval. Optionally, feel free to spread the word on your new flag or sail and get some votes for the sticky thread where people will do just that -- vote on your stuff!
Flags and sails aren't the only things you can create, submit and eventually see in-game. Flying Lab Software also loves it when you design and submit ships as well. This could lead to some very cool community projects in the future. Unfortunately right now the ship forums are a bit sparse, mostly due to a forums move that happened a while back. We think that given the creativity of several other MMO communities, it's not unreasonable to expect some truly amazing designs from the ship-obsessed fans of PotBS.