I thought it'd be interesting to try and compile all the Easter eggs that have been found in Firestorm - perhaps if enough people have found different ones, we might be able to piece together some of the background of Halvøy and Firestorm as a whole.
1. To start: SULIS (or SOLIS possibly - I'll call it SULIS through the post for consistency bc I can't remember which it is). If you've played even just one round of Firestorm, chances are you've noticed the SULIS logo dotted around - it's on the wooden strongboxes, the armour plates, even I believe on the premium Firestorm Ranger torso. What SULIS is exactly, no-one seems to know as of yet, but my guess is that it's an acronym for some sort of secret organisation that is based in Halvøy. It's probably fair to assume that they've got something to do with the fire storm, and the vehicle lock ups - perhaps even the little military outposts dotted around the map. I think it may be a sort of overarching Easter egg, similar to the Phantom program from BF4.
2. The generators around the map. These definitely have some link to SULIS - given that they've got the logo printed on them - but again, their purpose is unclear. It's worth noting that although they appear in clusters in built up areas, there are also some strange spots where there appears to be a generator out in the middle of nowhere with a ring of scorched earth around it. Did these generators somehow create the ring of fire? Who knows.
3. The objective balloons. These ballons could be just objective markers, but I want to say there might be something more - again, related to SULIS. However, they could just be the same sort of ballons that were raised during the Blitz of London to deter or disable bombers - I'm not sure.
4. Honestly, there's some more elements of the map that I could question and potentially link to SULIS, but without knowing more about what that is and what it stands for, I can't say anything for certain. For example, the secure vehicle breakouts - why are there heavily fortified bunkers set into the ground? Also, the POI named Pluto (Dig Site A). Is that just a quarry, or is there something else going on? I suspect more will become clear later down the line.
That's all I can think of in terms of the main Easter eggs, but as well as that style Firestorm is certainly full of other smaller, unrelated Easter eggs. For example, yesterday in the small group of houses a little north of the Minerva Docks, I noticed a small wooden door built into the concrete porch of one of the houses. On further inspection, I noticed there was a little stuffed bear inside - just a fun little thing to find, and there are actually I believe similar teddy bears on other maps, like a Twisted Steel at the top of the bridge.
Feel free to add any Easter eggs you've found while playing Firestorm, whether it's related to SULIS or just fun little map elements like the bear.