I think it depends on how long the horizontal run to the vented main is. I don't recall the exact dimension, but I believe this is called the 'weir', and the permitted length is determined by the diameter of the horizontal pipe.
Then again, I think what you have is a 'full S trap' and that they went out of code some years ago.
Red is right that is a full S trap and it is definitely no longer (probably in the last 75 years) allowed by code.
This is a trap that can siphon itself and allow bad stuff into your home.
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I'm thinking May Be, if the down pipe ties into a vented line.
Is that possible or this is just plain out of code?