First, have another centaur:
and a sphinx, which oddly enough is not one of the original monsters:
Now, continuing with the OD&D Critters:
Not that imposing, but as always I'll keep an eye out for something better. And for pirate, I think the most iconic representation is going to be in 17th century dress, with firearms. That won't work for most D&D games. How about a compromise, and use of the skull and cross bones:
These were made from Emanuel Wynne's flag. God bless Wikipedia. Not really silhouettes, but they should function to mark areas of pirate activity on your campaign maps.