Hi, this is mny first post here and I, sometimes, use a proxy for an anonymous navigation.
I noticed that some sites are able to "see" I'm navigating behind another IP. How to block it please?
The short answer is that you can't. Proxies hide your IP Address and identity (depending on how the proxy works), but they still have to provide their own identity in the network traffic that's used to connect you to a forum, or a Web site, etc.
In the same way that we here at WIMI can provide you some information about IP Addresses, hosts of sites that care about users of proxies can also determine the IP Address from which you are connecting, and see that the address is operated by a proxy service.
On the Internet, *everything* has to have a return address, or it wouldn't know how to get back to you. And everyone can read that return address.
Also, for your information, I deleted one of the two posts you submitted, since they were identical.
Generally speaking you are not more likely to get an answer if you post to multiple sections within a forum. In fact, some people consider that a kind of spam, and will ignore it. So you're actually LESS likely to get an answer in most forums.