I wish there was a standardized way to let folks who run a website such as this one know how much a casual passer-by viewer enjoys the byproduct of their work.
If you're in the EU (particularly Germany, France and Italy, who are the three largest funders), you can let your representatives know you appreciate ESA's work.
Thank you for reminding me! Just sent a couple of emails to my representatives!
Esa has social media accounts, pretty sure some intern will see if you ping them, I don't imagine they get much traffic
You used to be able to sign a guestbook
There is. It's called dwell-time
You might be staying there a long time because you're fuming, so: nope.
You are of course right that there are lots of potential motivations for spending extra time on the page. But it will likely be interpreted as enjoyment in the absence of other feedback mechanisms.