till I checked in to a hotel in Anchorage and discovered an envelope beside my bed with a typed message exhorting me to put money in it for the housekeeping staff "because they do a great job" or something like that.
That's really pushy, and I don't blame you for not tipping.
As for your question about tipping housekeeping staff in hotels in the US, here is what I do. I leave a dollar for an ordinary one night stay where I made no demands on the housekeeping staff. (No requests for extra towels, etc.)
For multiple-night stays, it is likely I have made some demands, so I leave proportionately more. I left $20 for a three night stay in Hawaii, where the housekeeper did a truly superior job and was super friendly, even greeting us by name in the hallway.
Tipping the hotel housekeeping staff is really truly optional. It's nice, especially if they went above-and-beyond for you, but not always expected nor always customary. I mentioned upthread that my husband went through college on busboy tips, so he has always been a generous tipper now that he has a college grad job and can afford to tip big. I do the same.
In my husband's eyes, every busboy, every waiter/waitress, every housekeeper is a struggling college student living on mac-and-cheese like he did when he was in their shoes.