This is assuming files aren't renamed from the download lol or used a separate downloader like RedditSave.
Title of the deviation followed with "by [artist name]" with underscores used for space then followed by an alphanumeric string: DeviantArt
Example: 'mordetwi__airplanes_by_bluedog444_d5a34hh-414w-2x'
Title of the sources post (dashes used for spaces (also title name ends prematurely if the title is too long)) followed by a '"v0" and an alphanumeric string: Reddit image
Example 1: 'quandale-dingle-restored-v0-yv9145ea62391.jpg'
Example 2 (Title cut off): 'has-anyone-else-noticed-that-ig-reels-is-turning-into-a-v0-qygr8vaqc6le1.png'
"m2-res_[pixel height of video]p" (sometimes contains the exact download time of the video after this): Reddit video
Example 1: 'm2-res_812p.mp4'
Example 2: 'm2-res_480p - 2026-03-11T171645.741.mp4'
This is all the identifiers of various websites that I know. Hope this can be of use to some of you guys.
Updated