./ is for the current folder
If that was needed I believe you can use ../ to go to a receding folder.
So using this case:
"./" is the start of where the cs directory is. So let's say we have a zip/folder as "Add-Ons/Weapon_Guns", but the weapon cs is in "Add-Ons/Weapon_Guns/Gun/Gun.cs", and your icon is in "Add-Ons/Weapon_Guns/Icons/"
Doing "./" for the icon will not work in this case because in that cs it starts with "Add-Ons/Weapon_Guns/Gun/" and your icon is in a different folder, so you would need to put the entire file location.
If you were in Weapon_Guns/Gun/ and your icons were in Weapon_Guns/Icons you could use ../Icons/blabla from within the Gun folder. I am not sure if this works in TorqueScript but it does in other languages so it'd make sense.