Assuming extra-terrestrial life (aliens) exist, what is the most likely scenario for them to make themselves officially known?

Across interstellar or interplanetary space, it would likely be a radio broadcast or flashes of light from a powerful laser.

At our planet, they have a number of ways to do it.

If they don't want their spacecraft to be too vulnerable, then there is a way: go into medium to high Earth orbit and then send out lots of atmospheric-entry capsules with messages in them.

If they are willing to risk provoking air-defense systems, then they can send some of their spacecraft to overfly several large cities at low altitudes around the cities' local noon.

If they want to land and let Earthlings meet them, then the best place is NYC Central Park. It's near the UN building, and it has plenty of open space. It is also surrounded by buildings whose occupants could easily photograph their vehicles landing. However, it's rather soft terrain, and if they prefer hard terrain, they can find some at three big airports nearby: JFK, LaGuardia, and Newark. If they prefer a water landing, there is plenty of water nearby that they can use.
Xendras
 
In September 2014 and September 2015, Paola Leopizzi Harris, who worked in J. Allen Hynek, who headed Project Bluebook, had an encounter with beings from Alpha Centauri.  They opened up a Xendra, which is an interdimensional portal, and invited Paola, along with a few others, to communicate with them.  Here is a link that better describes Xendras:
 
"Xendra" Domes of Light: Mission Rahma's Dimensional Portals
 
 
These beings have communicated that this work we are supposed to do is about us, not about them.  It's about the future of humans and our role in the future events.  I personally believe that these events have to do with the return of The Brotherhood of Light also known as The Great White Brotherhood.  In The Book of Knowledge:  The Keys of Enoch, is prophesied that in preparation for their return to the planet (a return which includes Jesus, Michael, Metatron, Melchizedek, Enoch, Elijah and many others), a delegation of interplanetary beings will land on Earth.  The Keys of Enoch state that "I saw how Man was prepared..."  I personally believe the encounters we are having with these beings tie into that.  The primary message of this movement is LOVE, PEACE and BROTHERHOOD.
 
Here are two videos from 2014 and 2015, which depict their vehicles:
 
 
Paola Leopizzi Harris is hosting a conference this November in Laughlin, Nevada, and I would encourage anyone who is interested in PEACE to join us.  We must prepare for these events through LOVE and PEACE.  The premise of this year's conference is art, music and consciousness and how these relate to the UFO phenomena.  Please join us:
 
StarworksUSA - Annual UFO Symposium
It's possible this is already happening.  In the past several years there has been a huge increase in UFO activity, crop circles and channeled messages.  It's like (presuming this is all true) they are making us aware of them through grassroots efforts.  This means that once the official announcements are made, we'll be ready.

See:

Ancient Aliens - the Mission
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