For some people, shul is a place to connect with their friends and neighbors as much as a place to daven. A smile, wave, or a whispered greeting should be enough.
If space allows, you may try to spread the word that you are trying to establish a silent section for those who want to better focus on the tefillah.
btw, this is the reason that I chose a shul where the women have a balcony. The space near the mechitza tends to attract the big talkers.