A practical puzzle for the internet age?

Happy Saturday everyone. I am waking up to the fact that someone is playing a head-scratching practical joke on me.

For the third time now I have received an envelope in the post of two (2) stickers. The first picture is the ones I have received today. I have no idea who is sending them but I have noted patterns in the three instances:

• There are always two stickers. One references a classic Vine (short form internet videos) and the other is a pigeon in various states of activity
• The envelope is always cardboard backed, post marked from Norwich sorting office, with a handwritten address and an ordinary sticker stamp
• The shipments are received from someone calling themselves "the Stickerman"
• The shipments arrive at roughly 2-3 month intervals

We have found merchants selling these stickers on Redbubble and Etsy but not all together which makes me think someone is buying them separately and putting them together. So I think "the Stickerman" is an alias rather than a seller.

What's leaving me totally scratching my head is the pigeon reference. I have plenty of in jokes with various friends but I can't think of any pigeon-related ones.

I have three suspects in mind:

1. One friend with whom we often reference classic Vines
2. One friend in a separate circle who is well known for jokes and hijinks
3. One friend whom I lived with at university, who may be getting revenge for a long-running practical joke I pulled in our final year

Number three is my current prime suspect as he lives in Norfolk, and we also used to watch Vines together over boozy nights. Alas he has denied all knowledge.

And so my weekend begins with a mystery.

Do any of you internet sleuths have any thoughts? Have you ever been the target of a long running practical joke? Or pulled one yourself?