No official statement or comment has been released regarding this sticker. Thus, we cannot confirm or infirm that this sticker is actually related to the Illuminatis. However, I believe there is a set of striking coincidences which point towards this sticker actually being a subtle reference :
- The colors perfectly match Iron Man and Captain America's color scheme (although simplified)
- The Ultron project is a global surveillance and counter-terrorism program which is intended to directly confront threats like Hydra, which is an Illuminati-like organization by itself
- Ulysses Klaue's file references the Bilderberg meetings, which conspiracy theorists believe is an Illuminati get-together.
Let's review these points in order.
1. The bottom part of the triangle is red and gold, Iron Man's classic color scheme. This could reference the Iron Legion's status as the "working men" of the Avengers, expendable units built solely as the Avengers' grunts and workforce. They perform non-combat tasks like warding off citizens. On the other hand, the leading man of the group is Captain America : he's the military strategist and moral beacon who ensures the cohesion of the team, and its ruthless efficiency on the field.
Tony Stark (aka Iron Man) is a founding member of the comics' Illuminatis, who represent superhuman communites (the Fantastic Four, Atlantis, the X-Men, mystics, the Inhumans, and the Avengers). The purpose was to share valuable intel about internal and external threats in order to protect Earth efficiently. Most notably, each member of the Illuminatis believe they are qualified to protect Earth in secret. As Black Panther tells them before rejecting their adhesion offer :
You just decided all by yourselves that you are the Earth's protectors. And that you, and only you, not your teammates or family, are trustworthy enough to include in the process...
2. In Avengers : Age of Ultron, the titular supervillain is created when Tony's hubris convinces him he can program and unleash a superheroic AI. Intended to watch Earth through every mean available to detect threats and eliminate them (or send rescue efforts in case of a natural disaster), it was in essence a benevolent version of Hydra's own surveillance plan. In real life, most of the Illuminatis' mythos revolve around their supposed quasi-omniscient surveillance skills, used to control and cull whole populations. Why ? Because they believe they are better than the common folk. Ultron's concept is (theoretically speaking) an Illuminati's wet dream.
3. The Bilderberg meetings are secretive get-togethers in the eponymous Hotel de Bilderberg, in the Netherlands. These meetings are real, and were first creating to strengthen bonds between European and North American leaders. As the meetings' content has never been made public, conspiracy theorists believe the Bilderberg group is akin to the Illuminatis, or ARE the Illuminatis.
In Ulysses Klaue's SHIELD file, we can read the following description :
Ulysses Klaue was an assassin hired to take down T'Chaka at the Bilderberg conference in the case that he refused to negotiate Wakanda's resources including Vibranium. But, Klaue was also there personally, as the Panther killed his great-grandfather in the 19th century while this one was trying to annex Wakanda. He was paid ten million dollars for the kill.
Put together, these thematic elements may point to the Illuminati sticker being a multi-layered reference. I would say its actual significance hinges on whether you consider the Bilderberg meetings to be Illuminati reunions or not. And, of course, it is highly unlikely any member of the cast of production team will ever confirm or infirm this, especially if they do intend to create their own version the Illuminatis later on.