yes but me and some others can't signs, we do not have this option for exemple with coinpayments (and some others too don't allow to sign, i'm using another for my bitcoin wallet and they don't allow to sign too).
the reply from coinpayments support :
"There is no way to sign messages with your deposit addresses. Remember never to do anything that would require you to sign from our addresses or otherwise prove ownership of them."
ok, so you can hopefully now see that there is no way coinpot can confirm that this address belongs to you - because it doesnt belong to you, it belongs to coinpayments as they have the private key
And the worst i tried to deposit to links account to coinpot, all depositing was credited on my coinpot account but it didn't link any moonfaucets and supports don't replys :x << and this is the problem >>
im guessing your deposit didnt link the address because the deposit was made from a different address. it clearly says on the coinpot page that you must make the deposit FROM the address you are trying to link
im sympathetic to your situation but there isnt anything anyone can do for you here.
i suggest you just sign in to the faucets using your coinpot account email instead of the wallet address - then you will get all your earning from now on
(plus : on my coinpot account the wallets address i use for withdraw are the same than my moonfaucets account for login since coinpot open...)
again, this doesnt prove that you own that wallet address so it doesnt help solve your problem