Going to Germany later this year. I've been seeing things about people getting stickers put on their passports when checking in at European airports for their flights back to the U.S.(additional security is what I'm understanding the stickers are for). I plan on checking in online the day before and only bringing carry-on luggage. Since it looks like people get these stickers when they check in at the airport, will I still need to go to the ticket counter in Frankfurt to get it (assuming that I do need a sticker) even though I will have already checked in online and not checking a bag? Or should I just go old-school and check in at the ticket counter anyway?

If you can check in online and are traveling with only carry on, by all means skip the counter. You may well be asked security questions about your bag (who packed it? when? has it been out of your control since? anyone give you anything to carry? etc.) at some point prior to actually boarding and those stickers put on your passport cover. If not, don't worry.

I was in Germany last month and I didn't get a sticker.

It may depend on your airline. We flew United last October and were told to go to a counter (staffed by United employees) across from our departure gate. We already had our boarding passes and did not have checked luggage. They asked us a few security questions and stuck a sticker on the back of our passports which was checked by the GA when we boarded. Folks who tried to board without the sticker were sent over to the counter. YMMV

Thanks, everyone! For what it's worth, I'm flying with Delta Airlines.

And what kind of stickers? I have never had stickers. And nobody gave them to me. And what are they for?

Ours were tiny round stickers the size of a collar button, which the agent initialed, showing we had "passed" the extra security questions.

We always seem to get stickers. They're hard to remove once home.

The sticker indicates that you have passed a security screening.

We've always had a complete opposite experience - never had trouble removing the stickers - they just peal off.

Our experience with international flights is that you cannot completely checkin on-line. Generally someone whats to see you passport to make sure it is valid. These little sticks confirm that it is valid and has been checked. I think it speeds up the boarding process instead of having the gate personal double check passports.

Now, the Dot-passport travelers had passports with dots.
The Plain-passport travelers had none upon thars.

Those dots aren’t so big. They are really so small.
You might think such a thing wouldn’t matter at all.

I never remove them -- don't get them all that often but right now there are 5 on the back cover of my passport, the earliest from 2015.

I had lots of them on my previous passport, I did not remove them as they were hard to remove without ruining the passport cover, bit like the baggage label receipts that sometimes get stuck on your passport by bag drop staff.