I get quite a few emails per hour advertising penny stocks. I never pay any attention to spam, but now and then I think about them for a few seconds before purging my spam box.
In the UK all stocks are quoted in pennies, so it's not £3.50 a share, rather 350p. I assume that the spam is some US thing where they trade in dollars not cents, so a penny stock is something very cheap, and under a whole dollar.
In the same vein I always find it funny to receive "lose 10 pounds" emails. To me, a pound is a monetary unit, which is exactly what you lose if you send them any money. Weights are measured in kilos.
Spam evidently isn't internationalised yet, though phising scams are.