Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision. Imagemagick...
Ed. 2d 91 (1992), the Supreme Court held that when an out-of-state mail order company "purposefully avails itself of the benefits of an economic market in the forum State, it may subject itself to the State's in personam jurisdiction even if it has no physical presence in the State."...