Praising student effort, achievement, and motivation is nothing new. It’s a basic tenet of any teacher’s arsenal of tricks. The strategic and/or systematic use of positive praise is a huge component in classroom management programs as well (especially by seasoned teachers). When used appropriately, positive messages can be a goldmine for students.
With today's challenges to your students, be proactive and provide a personal note that will create a memory that can refocus their attention and be life changing in many cases. Don't underestimate the respect that a student has for their teacher! (aka Hero)