If your server is 1.7+, you are able to set a server icon. Here's how to do that:
1) Generate an image that is 64x64 pixels. You can edit the image in Paint or using a website like this one to change the size to 64x64. Right click the picture and hit view details to see the image size.
2) Name the file server-icon.png exactly. Don't include any capitals and be sure to have the -.
3) Put the file into your server's root directory (the default location when you go into FTP, without going into any folders) and restart your server.
4) Wait a few minutes and refresh in your server list and the icon will show up if you have done everything correctly.
