Many people have wanted to get involved and enjoy Pirates of the Burning Sea's user-submitted content system, but as things currently work, the turnaround time between submitting a flag or sail design and actually being able to purchase it in game has left something to be desired. Thankfully, Flying Lab Software realized that this situation needs fixing, and have announced that User Content 2.0 is on the way.
This re-haul of the user content submission process changes the way that player's designs are voted on and approved. Other players will be shown two different designs at a time, and will have to choose which one they think is better/more appropriate to the time. After a design receives a certain amount of winning votes, it goes off to be approved by FLS. To be able to submit more designs, players need to spend some time in the voting process, so there's incentive to do the sorting work. Some other changes to how you can show off your work in the forums are also detailed in the User Content 2.0 announcement.
We haven't been told when exactly the new system will be in place, but for now the old process is still in use. Don't forget that if you're that little bit more adventurous, you can submit a 3D ship model as well, and if this intrigues you then check out the Shipwright Discussion forum -- you'll be in good company.