Hi
You can use
Event.Source member from the Symbol browser to get the source of the event that triggered the policy.
To have a policy check this value for all WWW Proxies, you will need to create a new policy based on the same event that is registered by the different WWW proxies, such as the ClientConnect or Request event. All of these individual ClientConnect or Request events will be available in the one policy since they are
deemed to be compatible. When each different WWW Proxy registers its version event, that instance of the event is identified by the proxy (source) that registered it.
Once you've created a policy based on one of these compatible events, simply place all the compatible event policy items (from the different WWW Proxies) in the policy editor on to the worksheet, and connect them to a policy item that will check the value of Event.Source (like Example 1 in the compatible events help link I gave above).
For example you could use connect them all to the switch policy item to check the Event.Source value (to discover in which proxy the event is occurring) and as a result determine which path it could go down. This could be calling into an individual policy for each different proxy etc, evaluating other stuff, incrementing a global counter to see/monitor per WWW service hit rate to a global data list so other policies, event processors can reference it, etc.