t.window.icon only applies the icon at runtime. It doesn't physically put the icon on the EXE. For that you need to use a resource editor on Windows or place an icon file in the .app bundle on OS X. I'd assume the icon size should be one of many standard icon sizes on modern OS' such as 128x128 or the like. (Usually a size like 16x16, 32x32, 48x48, 64x64, 128x128, 256x256 or 512x512. At least on OS X. Not sure what Windows' maximum icon size is.) Probalby something small though since it's only placing the icon in the OS UI while the game is running. (I believe it refers to the icon in Windows' titlebar. OS X doesn't utilize this so it doesn't apply there.
The Wiki doesn't clarify anything at all that I can see.
Personally I don't see this as an important feature at all. It's just the tiny icon in the titlebar. People won't really be looking up there expecting a custom icon. It's just there as an extra touch.
oh i see what you mean well i have a mac i am not using windows
not sure how to do it with mac i can tell u see tutorials for windows but for mac not much unless i haven't search deeper..
Well, which one are you trying to do? setIcon doesn't do anything about changing the icon on the application in the Finder. It's only for Windows as it changes the system icon in the top corner of the window. TO change the icon in the application for creating a finalized game bundle it's easy as long as you have a proper icon creator. (Install Xcode from the App Store and you can use Icon Composer) The icon would go inside the love.app file (folder) under /Contents/Resources as Love.icns. The shortest method to do this once you have the .icns file is right-click on the love.app bundle, select "Show Contents" then navigate through Contents > Resources and replace the existing Love.icns file. There are other steps to finalizing a project though so just changing the icon is not the end of things. (Modify the .plist file to change certain things so the love.app is no longer Löve and associated with .love files for example) There's a thread somewhere here for doing this stuff. But you shouldn't be thinking about that stuff until you have a finished game worthy of uploading as an actual executable. For most cases you can just upload a .love somewhere and put instructions on where to acquire Löve for running it. If it's a big game like Mari0 then of course you can have the Windows EXE and the OS X .app ready for users as well as a separate .love source for Linux people.