In Teamspeak 3, you have the option of setting your own icons for groups and channels. To do so, proceed as follows:

1) Right-click on the channel for which you want to set an icon.

2) Click "Channel Permissions".

3) Then open the menu point "Group".

4) Double-click the permission "Icon ID" and a new window will open. It is important to double-click the "Value" field.

5) In this window you can now select an icon and even upload your own icon. Once you have chosen an icon, simply double-click it. The icon will now appear to the right of the channel.

It is the same for server groups, except instead of editing "Channel Permissions", edit "Server Groups".