I think there was a thread like this on the old forum, either in the international or in the German community part. Let’s revive it! 
You know you’re a Postcrosser when…
…every friend or relative brings you postcards from their holidays.
…you buy new stamps the first day they’re out.
…you run out of boxes for your written and unwritten postcards.
…you can’t visit a postcard shop website without ordering “just a few cards”. 
When do you know you’re a Postcrosser?
You have a card written and stamped within minutes of having one received! 
Your postal worker knows you by name.
Your Amazon/or general wishlist is all postcard boxes, books, and special pens, stickers, washi tape, etc.
You cannot pas any store without doing your mental checklist:
Might they have:
-cards?
-stickers?
-stamps?
-washi/other decorations?
no? do checklist for next store
Better yet, since you can create multiple Amazon wishlists, you have one dedicated just to Postcards, one just for Stickers, one just for other ‘Snail Mail’ supplies, etc.
True!! My family has a “family wishlist” on Amazon because it’s easy for relatives to look for one wishlist instead of four. But, I have my personal “shopping list” of postcards on Amazon.
Offtopic, but: beware of feeding a monopolist - in the end they might eat you
You know you’re a postcrosser when you can comment places mentioned in world news headlines with ‘have sent there half a year ago’.
When you tell yourself you don’t need to buy any more postcards…but maybe just one more, and oh that set, oh and maybe that one too…
You know you’re a postcrosser when you go on a day trip just to buy postcards.
(I had train tickets and a day off to go to an essential appointment in London that wasn’t needed in the end. I still went. I spent two hours in the British Museum, bought some postcards, had a KFC and took the next train back to Leeds.)
// This was two years ago in case anyone wonders! I went to renew my lost passport and then found it the day before I went…
I live in a big house whit many postboxes, first comes the newspaper together whit some advertising magazines, mostly they lay a bit outside. Since I get Postcards the newspaper isn’t anymore pushing in for the letters. The postman take it out, put letters and postcards in and refills the newspaper. 
YKYAPW …
… local landmarks you had stopped taking notice of suddenly become interesting again as it’s super fun to tell fellow postcrossers a bit about them.
you have a memorized answer (possibly even in multiple languages) explaining why you get so many postcards. From strangers. Who got your address off the internet. No, it’s not creepy.
your dreams now involve a whole lot more postcards than they used too.
fetching the post isn’t a chore anymore.
your tiny niece thinks that going to the post office to drop off cards is just something that everyone does daily.
you spot a lovely postcard in the secondhand shop (that you visit mainly to look for cards), and are disappointed when it unfolds into a greeting card.
when you know your country’s postage sizing and pricing a little better than you should (i.e. by heart)
when “scanning postcards” is a legitimate thing on your To-Do list
you go to post a regular letter, and feel a shock for a second that you forgot the Postcrossing ID before remembering that not everything needs one
Just a few days ago I dreamed that I went to Tanzania and stressed out about finding and writing cards immediately. When I told my boyfriend about it, his answer was “yea, sounds like you”. 
You have stacks of postcards from people to write back, thank and register. It helps if they put their username and the website. It’s a plus if they uploaded the photo of the card for the wall already.
…and relying of having something else in the mailbox than bills, official letters…advertisings…
feeling bad when putting the account to inactive because of moving…
fretting about not getting post due to the planned move…
thinking about the “right” stamps…
One of the greatest reliefs is when the card that has been traveling the longest finally gets registered.
When you feel the need to write an ID on every piece of mail you send out.
Or when this happens… (The postal staff using a rubber band for all your mail.)
When your mail carrier sends you a postcard to thank you for the treats (cooler with snacks and water we started putting out in the heatwave last summer and continue to do, plus gift cards for holidays) because he knows how much you like postcards!
Also, because you are often snapping photos of the address part of the postcard in front of the blue box to confirm swaps and trades.
… when you are on first name terms with all the workers in the postal agency.
… when you get your neighbours postcard in your letter box because the postie didn’t even think anyone else in the street would have some.
… when you get excited over the sticker department and you don’t have young kids anymore.
… when you find yourself handing out pieces of paper with postcrossing.com written on them to anyone who shows a remote interest in your postcard habits.
… when you are going out of town for a few days and you worry that your postcards aren’t going to be registered straight away.
and yes on the rubberbands around your mail!!
