You need to prestige each individual weapon to put both the emblem and the clan tag on in.
For example. If I prestige my pdw once. I can now put my clan tag on my pdw. Prestige it a seconds time now I can put both my clan tag AND my emblem. But only on my pdw.
After you do that move on to your next preferred weapon and repeat!
Pro tip: if you get a weapon prestiged twice you get an awesome new calling card! And if you do all of one weapon type (like all smgs) you get diamond camo!!!
Haha have a good one.