A tagline is usually a businesses or personal mantra, and helps people see what you're about, evokes an associated emotion and, is memorable.
The biggest brands have them, "Just do it", "Snap Crackle and Pop" and "Think different" to name but three. Where I work right now the tagline is in the image below: Grow Greatness.
Many of my favorite thinkers have them too
"You’re awesome and you're doing great" is how Michael Bungay Stanier closes almost all of his communications
"Stay awkward brave and kind" is how Brené Brown closes her podcasts
So what will your tag line be?