Paint.net, basically just a better version of paint. You can do layers to help position things better without effecting the other parts, like the text

What program do you use?

I ment I send them from my phone to my computer through discord

I take 2 screenshots, 1 of the front with them on the left of the screen, then rotate for a profile shot and move them to the other side. I then send both screenshots to my wife's psn and use the PS app to download them, send them to discord to get them onto my phone. After that I use an image editing program and do it all that way.

I wasn't referring to decals, I was referring to the AC4/4A like representation of the assembly. I was just wondering how OP went about making them.

It helps to mess around with the shapes available. Just rotating and changing the size and putting them together can get you some interesting images. Messing with the gradients can whole dimensions to them. I think there are tutorials of learning the basics of it. What also helps is to go by an image you want to have as an emblem and selecting the best shape and size for each part of the pic.

How do you make these images? I was thinking about making my own