How can I tell if someone blocked me on Twitter?

[Samantha]

I'm following Genevieve Padalecki and Jared Padalecki on Twitter. Everytime I tweet Genevieve or Jared, I don't see if my tweets got sent to them. Do you think they both blocked me? I am a fan, a BIG fan of Supernatural. And I've told Jared and Genevieve that. I told Gen I liked her acting as Ruby on Supernatural. She's got real skills. Anyway, can anyone tell me how to know if someone blocked me? Thanks!

[Halloween66]

If I was Following them when they blocked me, the big blue FOLLOWING button changed to FOLLOW when I reloaded the page. So, that’s a tell. Mind you, Twitter sometimes spontaneously unfollows you from people, so you should click to Follow them and…
When I tried to Follow people who’d blocked me, I got a little “Sorry. You can’t follow that person because they have Blocked you.” Pretty straightforward.
If I was not Following them before, their page looked exactly the same and functioned as above: when I attempted to Follow I got the message I’d been blocked.
Their old tweets remained in my stream.
Their new tweets didn’t show up in my stream, even when they @’ed me. But other people COULD rt them and then they would show up in my stream; I suspect this depends on how that rt’er is using Twitter: web Twitter, Hootsuite, Tweetdeck, or various other apps.
Interestingly, if you’re using web Twitter and click on the username somewhere in your stream and the person has Blocked you, you get the little pop-up snippet of their profile page, but if you were Following them when they blocked you, you still appear to be Following them; the big blue Following button is on the pop-up, but not on the main profile page, so always go to the profile page to check.
If I was on their profile page and tried to rt or favorite a tweet of theirs, I just got a generic “Sorry, we’ve done something wrong. Try your retweet in a few minutes”.