1) All-seeing eyes. Usually in a triangle/pyramid (symbolizes horus, an Egyptian idol), but not necessarily! One lone eye could still symbolize it (incl two-eyed creatures with one eye covered by something). Not taking it to extremes, of course. Not every instance of this is a sign of something.
Examples include the U.S. one dollar bill, Bill Cipher on Gravity Falls, the doodle god logo, etc.
2) Hexagrams, 6-pointed figures.
Examples include, once again, the U.S. one dollar bill, possibly Twilight Sparkle's cutie mark on MLP, the mason logo seems to suggest a hexagram too, some of Bring me the Horizon's merchandise, etc.
3) the words "rain man" or "rain". I know the word "rain" is a huge stretch, but you'll see it. When it's used in negative stuff, it's usually a metaphor, usually for evil. And "rain man" is apparently another name for the adversary.
Examples of that seem to be all over popular music. An example of the rain metaphor could be these lines: "Feel the rain on your skin, . . . only you can let it in . . . Drench yourself in words unspoken"
The last part suggests negativity because of, well, the context, and also because the positive word of God has already been spoken. It's not about "words that are unspoken" like in the song. I know it seems subtle and nit-picky, but it's kind of not.
4) Lightning bolt symbols. When they're used in negative stuff, they're usually one of two specific shapes, one that's shaped kind of like an "S", and one like that but with an extra right, and down-left line at the bottom. Lightning symbolizes the adversary from when Jesus said, "I saw Satan fall like lightning from heaven." (Luke 10:18)
Examples include the logo for the computer program Daemon Tools, Pearl Jam's album "Lightning Bolt" (also has an all-seeing eye), the promo images for Arch Enemy's "War Eternal" (also had all-seeing eyes), etc.
5) Black, white (or gray), and red solid colors together. Usually not blended. Just solid, contrasted colors like in MS Paint or something, though that's not always the case. I'm not sure at all what the significance is, just that red is often associated with evil, I guess. I don't know what using solid colors is supposed to mean.
Examples include the aforementioned Pearl Jam album, and basically any album art you see with those colors made after, like, 2010 or so, particularly if the band or artist never used those colors before.
I know there are a lot of other ones, and I'll update this later with more. In the meantime, I pray that these five will be useful to you. In Jesus' name. Amen.