My wife has one of those black boards with little white plastic letters that stick in between folds in the board (sorta like this) that she changes the message on every week or so.
One of my first projects was printing a dickbutt the exact right scale and with the proper little tabs on the back and sticking it up there one night after she'd already gone to bed.
Then I waited.
Bought this letter board on Amazon to hang on the wall behind the taps to display what’s on tap. It’s simple and clean
Amazon! Felt Letter Board with 680 Letters, Numbers & Symbols 16 x 12 inch :: Changeable Letter Board for Quotes, Messages, Displays, Words & More :: Hangs Or Stands Alone:: Includes 2 Storage Bags (Black) https://www.amazon.com/dp/B07CYZKDCW/ref=cm_sw_r_cp_api_i_WEiiFbGE95996
A bit smaller but might work and should give you some search terms for looking for aaaaaa larger version - https://www.ebay.com/itm/Changeable-Letter-Message-Counter-Sign-400-Letters-Numbers-Characters/302966150399
Larger size from Amazon - https://www.amazon.com/MasterVision-Letter-Board-Black-Aluminum/dp/B00MV1NTL8
If you're worried about people mistaking your door, why don't you get one of those stick on hooks and a sign that says "(Your Name)'s Room" on it? https://www.amazon.com/dp/B07LGFQVM3
Otherwise just get a chain lock: https://www.amazon.com/dp/B00QRZAVOW
Steal away, definitely not an original idea haha. :) I was gonna have the announcement be all 3 of our cats saying were getting them a pet human but realized there's no way I could get all 3 to cooperate for one pic. Hubby and I are huge nerds so this was the next idea we liked. If you haven't bought a board for the announcement here's the link for the one we used, highly recommend. Comes in super cute packaging and they give you a crap ton of letters/numbers in a cute case to use and it's a nice size. Felt Letter Board 10x10 | +690... https://www.amazon.com/dp/B075JG2MVQ?ref=ppx_pop_mob_ap_share
My 14 year old daughter loves playing with a felt letter board. She makes nice messages anytime someone comes to visit. Here is a link to the one I got my daughter: https://www.amazon.com/dp/B078QD85P1
Changeable letter board. There are many shapes and sizes. Different fonts, etc