Understanding the current King, his relationship with modern Thailand, and the context for royal reverence.
The current King (ascended 2016) is a different figure from his father — he spends significant time in Europe and has a complicated public image both inside and outside Thailand.
Lèse-majesté laws (Article 112) are among the strictest in the world — prosecutions have increased in recent years; foreign nationals have been charged.
Yellow and white flags on royal birthdays; the national anthem played at 8 AM and 6 PM at public venues; portraits in all public buildings, shops, and many homes.
Simply respectful behaviour is sufficient — no need to understand the politics; stand for the anthem, don't criticise the institution publicly, and you'll have no issues.
Royal portraits in shops and offices, the anthem playing in BTS stations and cinemas, and the widespread use of royal colours on significant dates are all everyday, low-key expressions of this reverence.
It's best to avoid initiating conversations about the monarchy with Thai acquaintances — a subject most locals prefer to navigate carefully, if they discuss it at all.