Facebook marketing team has released posters that you can use in your business stores after printing them. Its PDF so you can print them and put it in your office, stores or anywhere you want to encourage your clients, customers and others who visit your business place to join your page on Facebook. Also if you like you may put it in your website linking to your Facebook page but these posters are better for using as printable posters and for websites those old Facebook badges are fine.
Download all posters from here: http://ads.ak.facebook.com/ads/FacebookAds/Facebook_Signs.pdf