Various 'Easter Eggs' can be found around Streamlined's map. These are references to inside jokes between the developers, and are generally introduced as rewards for contributing to the game. The locations aren't listed so you can find them yourself on your adventures.
Blahaj

This little guy has been on dry land for months now, quick, bring him some water!

Brandon's private room
Brandon is one of Streamlined's testers and contributors. As a little thank-you, his Roblox avatar has been placed around one of the stations. Whereas it used to be in a building's attic with part of the roof missing, he's now sitting comfortably in the station's toilet.
Cheeselined

Quite possibly, most of us have often over-looked it. Just like Minceraft, in Streamlined there is the off-chance that you might receive Cheeselined. The rarity is great: If one were to repeatedly open the game in the span of 36 hours, they most likely would not see it!

Developer Statue
Whilst not a very well hidden easter egg, this statue shows some of the current and retired developers who have helped bring the game to where it is today!

Doggo Cow
Doggo Cow has the shape of a regular Streamlined cow, but the texture is a well-known picture in the Streamlined Community. The little rascal likes to hide in a herd of regular cattle and will occasionally find a different herd to stay with for a while.

King's cone
This crown worthy of kings and queens adorns the head of the statue of King Willem I. This is a reference to BuilderAtWork's iconic blue traffic cone avatar.

Palace party
When standing around the palace, Spongebob's "Jellyfish Jam" can be heard playing on loop inside the palace. Whilst noone is invited inside, the music is loud enough for the crowds outside to enjoy.

Peperga chairs
One of the easier easter eggs to spot, this is a nod towards the rattan chair factory that was located in Peperga. They used the local goods shed to store and eventually ship their chairs to various locations in the Netherlands.

Piels Shed
The location where MPiels often likes to hang out. MPiels made this model himself; It is a replica of his own garden shed.

Smoldrinsk
Emil has been out at night vandalizing the neighbourhood. This text is a reference to the pre-rebuild Voorlem Oost, when this part of the city looked very much like an East-German city in the 1960s.

TheModsterRB VS Jensen
Is this a JoJo reference?! As these contributors couldn't really fit on the statue nicely, they received their own display.