Hi. I noticed certain skins (blackhole for example) were incorrectly displaying my sd channels as 576i (PAL sd). NTSC/ATSC sd is 480i. I noticed skindesigner itself didn't have NTSC/ATSC sd support so I patched it and modified the ico_sd576i.svg icon for 480i. I sent both the patch and icon to Louis for his review/commit. I figured I would mention this here as well so anyone else using icons to display resolution will know to include an ico_sd480i.svg (or whatever) for non-PAL users. 
Thanks