The Traveller Folders is a nice collection that provides personalised folders in order to sort your pictures by country.
Choose the folder you want to custom, press CMD+I (informations) then drag and drop the flag icon in the original icon on the top right corner of the information window.
The pack includes the following flags: American, Austria, British, Croatia, Cuba, France, India, Israel, Japan, Latvia, Macedonian, Madagascar, Maroccan, Dutch, Norwaygian, Palestinian, Philippinos, Portuguese, Serbian, Singaporian, Slovenian, Spanish and Swiss.
The Jolly Roger as the original Photoshop PSD file so you can do your own version: simply add a flag as a new layer, create a clipping mask then set the layer in overlay mode and it`s all done.