A meme can be as simple as making neat folds in the end of the toilet roll in hotels.
As you have identified regarding the watchtower, religious ideas are also a meme.
Dr. Susan Blackmore , a self-declared memeticist, describes memes thus:
"Memes are habits, skills, songs, stories, or any other kind of information that is copied from person to person. Memes, like genes, are replicators. That is, they are information that is copied with variation and selection. Because only some of the variants survive, memes (and hence human cultures) evolve. Memes are copied by imitation, teaching and other methods, and they compete for space in our memories and for the chance to be copied again. Large groups of memes that are copied and passed on together are called co-adapted meme complexes, or memeplexes."