Celebrating one's friendship does not have to mean just exchanging bracelets or rings. Tattoos are great for remembering anyone of the camaraderie that was spent with a friend. In fact, so many fraternities and military organizations have used tats as a symbol of unity. Only now that the society has actually eased up and allowed ink on almost anyone were we able to take advantage of tats for to symbolize that bond with a friend.
There are two ways to get a friendship tattoo. You can either have the same design on the same place or retain the same design but have it anywhere you want to. You can cook up a special insignia that will mean nothing to other people but represent your friendship perfectly and have it on the same part of the body like your foot or your arm. This gives a feeling of the feeling of likeness because you have the same art on the same part of your body.
If you are into the same interests, you can have an image which you mutually feel strongly about as a design. This can come in the form of a dragon if you both have oriental roots.
If you want a more traditional approach, you can actually have rings tattooed on your finger or a bracelet on your arm. You can choose whatever design like what you would have if you were actually purchasing the real thing for each other. This approach is so much better than the original one as you never will have to worry about losing the bracelet or taking the ring off.