Does this type of scam exist?

Yes there are many scams like what you describe. Criminals like money, and as one movie villain said "the best kind of money is .... other people's money!"

Popular game and music codes are easy to convert back to money. It is easy for the scammer to resell these locally.

It is difficult to tell what the scam is from your description, but fake romances, fake charities, fake immigration documents and pretty much anything fake is a possibility. Sometimes the fake is like an adventure, and real money is needed to complete the fake adventure, or to avoid a fake danger (oh, a corrupt official needs a bribe, oh his superior found out and now he needs a bribe too, etc.).

Many scams will escalate from small favors towards larger ones (money for a plane ticket or travel-related emergency for a romance or to help a sick child for fake charity, perhaps) until the victim blows up. Keep in mind that scams can work because people want to believe the scam (a fake romance with a doctor; $100 million of found money), or because of threats or extortion, or for other reasons.

So as a minor, your best course of action is to first involve your parents, then involve your extended family members such as aunts and uncles. Sometimes, a counselor or teacher at school can help, or a policeman or policewoman. The polite way to do this is by expressing concern and asking polite questions. Pictures of the codes and receipts, or screenshots of what they cost, may be helpful in convincing family members about your worries in the case that your mother is mentally tricked by a scammer.

Sometimes families or even the police may not be immediately helpful. But whatever you do, do not communicate with the scammers directly. If the scammers interact in person, that would be a good reason to talk to the police because that is a more dangerous situation than being scammed over the internet.

I suspect you may know this already -- the internet is a public place, and criminals read the internet. For that reason, you should not post personal details such as your home address, email addresses, or things like that anywhere on the internet, nor should you PM those things to anyone.

Uhmmm... what if your mum is the scammer? The evil one? Let's try a different interpretation.

I won't focus on the African friend part, but on this

I heard her talking about paying for this "signature" and to send the money over so that some people could forge this signature so that he could then send some money over

To me, this sounds like a fake cheque scam. According to my information (not verifiable), banks don't have a strong tendency to perfectly match the signature on the cheques with the specimen provided by the account holder. A counterfeit signature is an easy task because it requires a forensic to be busted.

There are a number of scams related to fake/stolen cheques.

This is extremely serious and needs to be stopped instantly - today.

I can only see two routes,

1. Immediately phone someone like an Aunt or Uncle, if there is such a person, and tell them everything.

2. Walk to the police station and tell them everything.

Your Mom is going to be pissed at you for awhile. You're just going to have to accept that.

Do 1 or 2 as soon as you read this.