As a very volatile month comes to a close, investors should take note and realize that this is a "very bad market," CNBC's Jim Cramer said Monday.
"The market's very thin. People are making a lot of big moves in a market that is not that stable, but I would point out that we have to get used to this. [S&P 500] futures were down 25 [points] last night and there was nothing going on," Cramer said on "Squawk on the Street."
Monday was the last trading day in August, and the three major indexes were all down more than 5 percent for the month.
"The carnage has been incredible, and we keep acting in this 'wait until you see what happens' mode. I take a look at the charts and I cannot believe what has happened," Cramer added.
"Is this a bull market? It's not clear to me."
U.S. equities opened trading sharply lower Monday.