What is it?

Many servers use their own icon. You can notice them when you use in-game server browser and look up server details. It also appears in your Rust+ app when you have paired your device with the server.

Server ConVar

You can assign a custom icon to your server using this convar in your startup configuration:

+server.logoimage <url>

It must be a direct URL link that leads to your .png / .jpg file. For example, "https://example.com/example/image.png"

Icon Preferences

Recommended image size for a custom icon is 256x256 px. In Rust+ app and in-game, icon is always displayed in a circle, which means that anything you have in image corners will be cropped out, so make sure that your logo (or anything else) fits the circle and it is aligned to the center. Here's a sample image:

You can also use this (unofficial) .PSD template for Photoshop.