If we become hesitant to become a rosary rally captain it is usually because the devil probably has tempted us to be afraid of what others will think.
First of all, under the protection of Our Lady's mantle, who cares what others might think?
Secondly, you will be surprised at the warm reception that you will receive. Some will give a thumbs up, others will wave, still others will hold their rosaries outside of their car windows. Because of your love and courage for promoting Our Lady, Her graces flow to all who see your rally.
It is quite uncommon though not impossible that some will react negatively to your public rosary, but the overwhelming response will be positive. One thing is for sure, everyone who passes by your public rosary will be watching you. No one just drives by as though you weren't there. Our Lady attracts passers by to Herself through the public rosaries.
Thirdly, when it gets right down to it, holding a public rosary is pretty easy. Think of the martyrs of the early Church and what they suffered for publicly proclaiming their faith. Think of the saints throughout history and some of their sufferings as a result of their public proclamation of the faith. Think of St. Thomas Moore. He could have caved in to public pressure and saved his life, instead he remained faithful to the Church at the cost of his own life.
None of us is being asked that kind of a sacrifice at our public square rosary. The most that we might have to deal with is a little bit of nervousness. If you feel nervous turn to your Guardian Angel, turn to Our Lady, turn to your Patron Saint and asked them for strength. They will give it to you. Once you begin your public rosary, I am confident that your nervousness will disappear as Our Lady's graces take over.