The closest I've found is objectual, but depending on the source, that may not be an actual word.
For example, if I were to refer to an author's use of symbolism via objects I would say something like:
The author is fond of ____ symbolism.
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Given that nouns can modify other nouns in so-called noun premodifier constructions, you might just go with object, as in
The author is fond of object symbolism.
Here are some examples where the phrase "object symbolism" is used:
This volume offers a number of new insights into the use of object symbolism
A philosopher who has considered object symbolism in a particularly profound way is Gaston Bachelard
Further, here are some relatively common phrases in which the noun object modifies another noun: