They are not prohibited by statute.
Leaving one on you porch, or bringing it to work, or in an environment where the humor will not be seen is not a good idea.
That's why they have the "hoax device"
https://malegislature.gov/laws/generallaws/partiv/titlei/chapter266/section102
(b) Whoever, without lawful authority, has in his possession or uses or places, or causes another to knowingly or unknowingly possess, use or place, any hoax explosive, hoax destructive or incendiary device or substance or any hoax chemical, biological or nuclear weapon,
with the intent that such hoax explosive, device or substance or weapon be used to cause anxiety, unrest, fear or personal discomfort to any person or group of persons, shall be punished by imprisonment in the house of correction for not more than 2 and one-half years or by imprisonment in the state prison for not more than 5 years or by a fine of not more than $10,000, or by both such fine and imprisonment.
So....your desk is okay. Jim's desk in the next cubicle....maybe not.