I'm not exactly sure how the coin is memetic… might want to read the Understanding Memetics guide if you haven't yet already.
I was under the impression that the transfer of an idea makes something memetic. Guess I was wrong. And yes, I have read and reread the guide.
Also, this seems less like avarice and more like extreme thriftiness (the whole "saving money" aspect as opposed to "gimme more money gimme gimme").
It's more about having money and material wealth, and the desire to keep it, and gain more of it. Although I'm fairly certain that the 'kill your family for insurance money' aspect qualifies as avarice. I'm not saying it's good advice (the coin is sapient, but it's not smart), but it is avarice. Fair enough about the title, though.
At its core, you have an object with a clearly defined activation and function, with no context or backstory, essentially a generic magic object. I recommend adding some more to this, because at this point the idea seems to be more of an anomalous object than an SCP that would merit specific Foundation containment.
What makes this more than a thing that does a thing? Was it created by someone? Was it ever special to someone? What might be the reason behind its existence? Does it have some sort of relationship with an important individual? Does it have a story before the Foundation locked it up?
It's a coin, which was produced by the Roman Empire, and got its anomalous properties during that time. I have some idea of how it got its properties, but the Foundation likely wouldn't.
The coin was owned by a citizen of the Roman Empire, who was an extremely greedy low-level telepath/mindreader who owned a shop. He would steal some goods off his customers while they weren't paying attention, and sell them later. He was eventually caught. Fearing execution, he tried to imprint his consciousness on a small coin he had in his possession. It wasn't much of a success.
I was considering adding another effect, but I wasn't sure if it fit. Basically, the coin would have a secondary memetic (assuming I'm using the word right) effect, that of giving those within a certain radius the idea of picking the coin up. The idea can of course be ignored, but the radius of the potential idea effect increases if the coin isn't contacted (and decreases once the coin is paid attention to), which would mean that the object can't just be left in a safe and forgotten about, and makes it less likely for the coin-bearer to drop it.
The coin was discovered after standard data-mining procedures found a spike in arrests, murdures and suicides within a certain city. Soon it was discovered that the incedents were focused on antique collectors, and a field containment team moved in (not an MTF. This isn't high enough priority or danger) to contain the object. And yes the coin has some history, but most people
Another thing I was considering was to make it a group of 19 silver coins (still Roman), with a presumed 11 out in the world, but it didn't seem like a good idea.
Also, keep in mind that the site already has lots of things that affect thoughts and things that make people potentially paranoid/unnerved/crazy 'till dead. Besides the whole "no action compulsion, just thought" aspect, what makes this unique amongst other mind-affecting items?
The idea is that it doesn't make the holder crazy until death or anything. It gives the holder a thought, an idea, and the holder assumes it comes from him/herself. The coin isn't forcing the holder to do anything wrong, but the holder sometimes does it anyway.
