Simple test, you post to a website which has the usual social media icons inviting you to follow said website on the social media platform.
If you leave a comment on the website, the date and time can be tied together with the social media platform. No need to send a search engine straight away, just linking the time frame to the appearance of a comment, over enough instances can link your website profile.

As Donald Rumsfeld said, there are Known Knowns, Known Unknowns, Unknown Unknowns and Unknown Knowns.

Time will tell.

Another simple test, you clear your cookies down, reset your internet connection to get a new IP address and visit a website (lets call it A) which sells something and you know is a heavy online targeted advertiser.

Now go off line, clear your cookies and go back online to get a new ip address.

Now without visiting Website A go surfing, how long till you see the adverts from website A appearing on other websites you visit?

This test can indicate your ISP is introducing a supercookie, but also demonstrates the US Tech giants have enough of an overview of the internet to identify virtually anyone.

Want to know how? Your display size is a metric, whether you use a 32 or 64bit OS is a metric as 32bit OS'es run faster than 64 bit. The browser you use which may be something you added to your device, eg Firefox on Windows. Have you over ridden any of the default settings in your browser? Are you using an Antivirus which advertises heavily online? What time of day is it, different times of day will eliminate other suspects from the equation. Are you browsing on a mobile phone? Do you have a mobile phone with GPS capability, have you downloaded any apps which have access to your contacts, text messages, emails, camera, GPS and other pertinent data? Does your mobile phone scan for other wifi networks to help geolocate you more quickly, like Google's Streetview car does/did?
Can you run JavaScript on your web browser? Web browsers don't hang on script bugs, using javascript to tell what version a browser is patched to can give greater detail than you see in the browser signature. Addons, what browser addons do you use? Did you know ad blocking/privacy trackers still report back information to the likes of Google? Have you set your firewall up to log and block all outgoing lookups when you use a webbrowser?
Theres so many ways to identify someone, its a bit like assigning a unique QR code to every person who browses online, where each block in the QR code is a different metric.

You have no privacy, and you can be tracked and traced by the US Tech giants as well as the spooks who have total oversight of the communication networks, even when your ISP gives you a regional geolocation.

So, seeing as this goes on, would you tolerate a load of Sandwich board men, following you around the highstreet into every shop, watching your every move, picking up items on the shelf and then as you leave the shop, those sandwich board men changing their advertising messages to reflect what you just looked at and picked up, as they follow you into the next shop.

Its like having www.GeorgeBamby.com following you around 24/7, watching you in the bath as you use your tablet, watching you at work, watching you as you take your kids to school and picking them up.

Its alright, he's only doing it for money, just like the online advertising companies and search engines are doing it for money, just like mercenaries' kill people for money.

Money makes crimes against humanity alright and you have no privacy!

Targeted online advertising is corporate stalking and harassment of intelligent people. If you are clever you would not put up with this type of cyber crime!