Exactly your dog is learning a behavior that will eventually translate into other things.  Our mark was initially a towel.  The desired behavior in any environment was to lay down on the mark, all the way down, head resting on paws, and wait.  The dog was learning to be calm.  To ignore the environment.  The towel in a sense became inconsequential, but it helped ground the dog in New exciting situations.  I have a high anxiety Aussie mix.  To this day, if she wants my attention, she will deliberately lay down on the floor in front of me, all the way down, head on paws, and stare at me waiting for me to praise her patience.  She doesn't jump.  She doesn't get up in my face.  She knows she has to bottle up her endless energy and be calm, and then we can do something fun.