Good Evening Jim my understanding is that you get the + in your tables when you use the Relationships Button under Database Tools and you setup a relationship between two tables as I have shown in the images bellow, I have never came across this in forms. Maybe someone's will chime in and prove me wrong.

Thx for your interest Brent.  I did find a resolve.  Hopefully this helps others..  In a form designed for data sheet view I inserted a sub data sheet.   In design view and then in datesheet view it appears as:  images to follow...

Good to know you showed me something I didn't know thanks for the info.

I really haven't covered this because I avoid using datasheet view like the plague. Too many problems with it when you start coding things. But if it's working for you, awesome!