Growing up I went to a bais yaacov school and we always said the pledge of allegiance in the afternoon in english class and we stood and put our hand to our heart.
I know people who put up an american flag on the fourth of July and Memorial day. Also in my neighborhood we have a parade on Memorial day and I know frum people who join in marching and watching and waving flags. It is to show the goyim that even though we are jewish we still feel for america.