I'm not sure but I think you can look for the hashtag #NOMOO or something
But, even if someone never actually builds with MOO enabled, I think the game will still give you that warning.
I know first hand that I have saved a lot before, never had MOO turned on, only placed objects on the default grid lines, and saved the lot to my personal library and when I went to place that lot in a new world, the game gave me that same error pop-up.
Mostly the problem with builders using MOO is the placement of objects can (and typically do) interfere with the function of interactive objects or routing issues. Builders use it because it makes the aesthetics of their builds look better, more lived in and realistic when cluttering stuff up, but for actual players .... it causes issues, unless that builder actually playtests all areas (which doesn't always happen)