Post a picture but the most obvious will be the chrome or lack there of. 150 doesn't have any, really. A 210 has a side stripe from stem to stern and chrome 'hips' on the back doors. Bel Air has the obvious spear on the rear and the same front as the 210.
My chevy book says that a 53 210 4 door is model # 2103. The 150 4 door is model #1503. But like Danimal said, 150's have no side chrome. That's the easiest way to tell.
as Dan said..unless somewhere down the line the stainless trim was removed.and filled in..than what 38 Chev said..look at the tag under the hood on the passenger side of the cowel/firewall area for the tag
150 4 door backlight does not wrap around, no horn ring, black dash knobs w/ no insert, no dome light switches in door jamb, black rubber only on w/s weatherseal, blankout for clock ...
Not always. Mine is a 210 and it starts with an L. Thats kind of like when people say that all of the hardtops were Belairs. They weren't.
heres a few pics...kinda dark but ill take some better ones later...ive only had it for about a week....so far ive done the brakes, ignition switch, starter.carb kit..spark plugs..oil...and the sucka runs good.