You have, and you should see it in the margin of your post above.
It's that thing that looks like a mis-shapen table tennis bat. Don't ask me why that represents 7 years, but if you hover the cursor over the bat, it will confirm it (on a desktop computer). I'm not sure how you "hover" on a mobile, but there's probably some trick which is likely to depend on the phone and/or browser that you are using.
You can also see it at https://community.giffgaff.com/t5/user/viewprofilepage/user-id/740337 where you get the option to turn it off (if you wish) and select any of the other stickers you're entitled to show.