This is how to add buttons into your Call of Duty: Modern Warfare 3 clan tag.
Text and video tut (run though can't show it as I dont have recording tools)

Video: Made by myself (TheGeekLiam)



To get this first go on your clan tag, Press RT then left stick down and you should get the accent letters in capitals. Press the A under the letter 2 then use the relevent letter below of which xbox button you want.

A= A button
B= B button
C= X button
D= Y button
E= LB button
F= RP button
N= Start button
O= Back button
P= LS button
Q= RS button
R= LT button
S= RT button
T= Up arrow button
U= Down arrow button
V= Left arrow button
W= Right arrow button
Extras: (not in video)
wont show up pm me= Trademark Symbol
wont show up pm me= Copyright symbol
wont show up pm me= Trademark Symbol

Then press start, Go back onto your clan tag and press start again, You can repeat this to get more buttons if you like.

Hope this helps and works out! Not sure if it's been posted before but here it is with all codes including the symbol ones! Will add more when more are found!

Cheers,
GOZZYxGOAT