I just do it for the fun of it, to add some whimsy, its something to work on during the exciting "anticipation" phase of pre-cruise. I don't get drunk on cruises (though I have often had enough that I would not have been legal to drive had I been on land) so the finding the door aspect is relegated just to a visual identifier from a distance for DS to let him know he's almost there--but he's a smart boy and knows his number, anyway.
I did signs on two RCCL cruises earlier this year, and was the only one with one, at least on my deck, on the Radiance and almost the only one on the Enchantment--there was a woman across the hall celebrating a birthday and cruising with many family members so they had decorated her door for her. Caught many people's attention, they thought it was fun to look at it was a common comment, and perhaps they'll do it for their next cruises.