These are 3D objejcts good for digital illustrators and comic book artists to incorperate into their workflow.

They are under licences with allow them to be to be referened, traced, and kitbashed into illustrations. Some models are licenced under CC-SA, which would require the final artwork to be CC licensed as well. Even if you're not a gamedev, you still need to respect the licenses of the art assets listed here.

Most art websites will give you a space for "author's comments", and that is the ideal place to give attribution. On websites like Twitter, creating a thread and including credits in that thread is the most common practice. If you offer art avalible for download, including a readme file in the download containing the credits is the way to go.

• All files (should be) avalible in the OBJ format. OBJ files are widely used with 3D programs that digital artists use. They can be imported into Blender, Sketchup (via plugin), and Clip Studio Modeller.
• 3D files must have a decent enough polycount to represent and detail the object depicted. Not everything is cutting edge with the polycounts, but nothing is too simple either. I love the low-poly style, but models which are too low in detail are typically unsuitable for art reference.
• Models with no textures and UV maps can be included. The expectation is that models will be referenced or traced, so their textures (or lackthereof) are unimportant.

• This list focuses on enviroments, and not characters. If you want to trace or reference 3D characters, look elsewhere.