definetly not the right choice of words, "we are invincible" makes it seem that they are all power, evil, and you cannot stop us and when your trying to recruit people thats definetly not the right choice of words, especially with the combine soldiers running toward the poster so it seems theyre running toward the viewer (and whenever a human looks at it, they feel that there is no hope for the human race.)
Because think about it, the Soviet poster with the words you chose is for the people of the Homeland, the people are HAPPY for their country and praise their country because its "oh so powerful"
The Combine on the other hand invaded Earth basically imprisoning them. It almost seems like a poster to break down the human races moral as living beings, if anything I would think it would depress a citizen even more and not encourage them to sign up. Even though your mentality would try to get the citizen to lose all hope and "if you cant beat em, join em" BUT since the humans are basically enslaved, one would think "I would rather sit here and rot then help those bastards"
i would try to create a slogan with a cross mix between the U.S. slogans to attempt to rally up citizens as well as a mix of slogans used in Germany ww2 for the "brainwash idea"
mabye something along the lines of "The Overwatch : See the world as new, join and protect the human race" (you could even enter in from themselves for a more "brainwash attempt") and have a picture of a Overlook soldier holding a baby standing next to a citizen family with them smiling, or 1 shaking hands with a citizen with the citizen smiling, or even have a Overlook soldier with his arm around a citizen lady crying with a "Don't worry, everything will be Alright" kindve look in his eyes and in the backround 4 combine soldiers arresting a male citizen in a alleyway with a evil look on his face. (to make it look like he tried to mugg /rape her but the Combine resuced her just in time and the male will be brought to justice)
But if you want to something with the whole Soviet propaganda mabye try something along the lines of
this.It translates to "The way to prosperite."
Also the pictures, they portray the Combine Overlook soldiers as aggresive and evil in a way. If you want to rally up and recruit people you have to make the overlook seem as if they are here to care and protect the humans, almost like a police force instead of a driven military who have to have a certain amount of beating quotas lol