Oke you asked for it, thou shall receive;
Take 2 pieces of rope or masking tape (in pics)of aprox 25ft and put tight on the ground (with rope use weights) about 2.5 to 3" apart like in this picture

Run bike forward, while sitting on it, till the end between the lines

Now check if rear wheel is centered.

This one below shows a bike that walks like a dog.

Do NOT rely on those marks on the swingarm.

Sorry about the picture quality due to compression