I sometimes add a space to help make the number more readable. Like the price for a share of S.MPOE is something like 0.00072828 bitcoins, you could write that as 0.000 728 28 to make it more readable. The problem with that is the space makes it hard to know where the number ends. An alternative would be to use ` (on my keyboard it is on the same key as the tilde, ~, but I never use it for anything), so the price would be 0.000`728`28 which is also more readable than having no separators. What is that mark even called?
` is a grave
´ is an acute