Funny, I'm in a similar boat. I'll never write the story, but I've mused on it occasionally. For me, the beacon was always a vacuum sealed warehouse 10m x 10m x 10m.
Start of the story, some boffin works out that colliding with air molecules will destroy any time machine going back, so he builds the warehouse, and posts the co-ordinates on the bitcoin blockchain.
One confirmation later, a time traveller arrives.