Have logged in yet this month and the News tab? There's a really cute Valentine's Day pun concerning the February 2014 Seal o' Piracy, where they represent this month's goals a motto on a conversation heart: "I DIG U". Get it? Because you earn this month's limited edition trophy by...
Completing 1 buried treasure expedition
Isn't that just precious?
It's also fairly easy. In 30 days of... well, 23 days now, since today's the 5th. OK. In 23 days of pillaging, the odds are good you'll snag a buried treasure map off some unfortunate brigand or barbarian ship. Probably those odds are better than at your Ocean's nearest Black Market, where laying down 10,000 pieces of eight for a black box nets you a 16% chance of containing any expedition map at all.
You can also haunt the Voyages tab watching for a pillaging job offer that specifies expeditions. Sometimes officers will start their voyage with several expedition maps, and they're happy to advertise.
Speaking of Valentine's Day, today's update to the YPP client changed out the seasonal content at the furnisher's and the Palace Shoppe. In addition to special Valentine's Day content, there's also seasonal trinkets, gifts, greeting cards and furniture items celebrating Chinese New Year. As of this writing, Yppedia does not yet have the full list of available items, so you'll want to log in and check out the inventory yourself.