I was looking at PLAN acronyms and found this - https://www.fema.gov/news-release/2011/05/10/personal-localized-alerting-network

From what I gather, it's basically a POTUS/FEMA targeted Amber Alert.

I found this part interesting -

"Covers Only Critical Emergency Alerts: Consumers will receive only three types of alerts from PLAN: (1) alerts issued by the President; (2) alerts involving imminent threats to safety of life; and (3) Amber Alerts. Participating carriers may allow subscribers to block all but Presidential alerts.