It means it’s Pentecost Sunday. And the folks who brought you #baconless during Lent are back with another Catholic meme. Just like the apostles went forth regardless of language, you’re invited to evangelize whatever your preferred social network. So on Pentecost, check in using hashtag #MassCheckIn whether you’re on Facebook or Foursquare, and tag a photo on Flickr or Instagram. See more info about #MassCheckIn.