What does Brutus mean by "rascal counters"?

When Marcus Brutus grows so covetous
To lock such rascal counters from his friends,
Be ready, gods, with all your thunderbolts,
Dash him to pieces!
During their acrimonious quarrel in Brutus's tent in Act 4, Scene 3, Brutus uses the wonderful term "rascal counters" as a metaphor for gold coins. By "counters" he signifies that these coins have no intrinsic value; they only have value because they can be exchanged for goods or services. They are like poker chips, which represent values attributed to them. The gold coins Brutus is referring to have images of men embossed on them, which tends to humanize the coins, making them seem like real men and, like most men, cunning rascals. Brutus regards the coins as "rascals" because that in fact is what money really is. Money doesn't care who owns it or how he acquired it, even if he did so by murder or theft. Money will serve whoever happens to possess it and will do anything for the possessor that money is able to do--which is a lot! Money can be used to bribe, or corrupt, or murder people. It is completely unscrupulous.
Iago speaks disparagingly of money in Shakespeare's Othello, although Iago, characteristically, is not being sincere.
Who steals my purse steals trash; 'tis something, nothing;
'Twas mine, 'tis his, and has been slave to thousands;
But he that filches from me my good name
Robs me of that which not enriches him
And makes me poor indeed.
Iago also is saying that money is like "counters" in being both something and nothing.