How to know if asm policy is referenced by one or more rules in BIG-IP?
I assume you mean Local Traffic Policies with "rules" and you are talking about virtual servers that have a more complex assignment policy, rather than the default ASM policy rule?
If so, you can have a look in the CLI, either via TMSH or opening up bigip.conf in a text editor and search for the name of the ASM policy.
For example, open CLI, then from linux command prompt; "nano /config/bigip.conf" and Control-W and type the name of the ASM policy. Repeating Control-W will let you jump through the rest of the config file.
Hope this helps.