How to tell if a proxy server was used

From the log file not the request

[aspdaddy]

I'm not looking for a 100% solution, or any software, just some ideas of what in the log file suggests a proxy was used.

Thanks.

[Dreamquick]

The only thing might be the rDNS name the request came from...

e.g proxy.someisp.com

There are a few more options if you have access to the raw headers but these are by no means foolproof, and they are not included in most logs...

[webmasterworld.com...]

- Tony