Yes I have this style of fix or panel clips. They are used to hold the sliding window panel in a storm in the up position.
Usually they are in pairs with one on the left and one on the right of the window sash. They also come with a spring which holds them in the closed position and a tiny retaining clip which fixes the spring in place on the frame.
There are hundreds of different shapes and sizes of panel clips, some aluminum and some plastic. Yours is one the more common ones.
I usually have 3 or 4 different styles which are the most common ones used in Southwestern Ontario Canada where I live.