The most common and most likely answer to this crossword clue is the 9 letter word OCCUPANCY
I've seen this crossword clue in The Daily Telegraph
O
C
C
U
P
A
N
C
Y
Buddy explains!

The straight part
We know that "sign of hotel guests" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sign of hotel guests = occupancy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OCCUPANCY mean?
OCCUPANCY noun- The act of occupying, the state of being occupied or the state of being an occupant or tenant.
- The period of time during which someone rents or otherwise occupies certain land or premises.
- The specific use to which something occupied is put.