Okay, I'm clearly not getting this one.
These old "romance" cards from the first part of the 20th century can be purely odd when looking at them over 100 years later. Some are suggestive. Some are coy. Some make no sense at all. I give you the following example.
The guy looks like he's about to thumb his nose to the dog with a "Naa naa, you can't reach me!"
I'm betting if this dog wanted to it could be over the fence and on that guy lickity split.
As to this message, I think it's safe to say it will never be decoded. It reminds me of one of those spy phrases you're supposed to say when you meet another spy. "Psssst. In the shade of the old walnut tree. Hurrah." Of course then the microdot is exchanged and everything goes along fine and dandy.