The removal of the plaque and the start of a fourth year under military rule marked a bleak chapter in Thailand’s history.
Thailand’s new king, Maha Vajiralongkorn, will pardon a number of inmates, including some jailed under one of the world’s toughest laws against royal insult.
There are fears among government critics that the military would delay a general election planned for 2017 until several months after the end of the mourning period for the late Thai King Bhumibol Adulyadej.
The attacks were the first since the death of King Bhumibol Adulyadej and defied a request by the military junta to desist while the nation mourns.
Bhumibol Adulyadej, who died at the age of 88, reigned for seven decades after ascending the throne in 1946.
The explosions happened ahead of a public holiday to mark the birthday of Queen Sirikit in Hua Hin, a popular upscale Thai resort south of Bangkok.
Thailand votes on Sunday for a new constitution that aims to subdue political parties and give generals a permanent role in overseeing economic development.