You may smoke unless otherwise instructed.
You may smoke unless instructed not to smoke.
You can smoke “unless otherwise told”/“unless told not to smoke.” then:
Unless “otherwise” = the opposite of “You can smoke”
You may smoke unless otherwise instructed.
You may smoke unless instructed not to smoke.
You can smoke “unless otherwise told”/“unless told not to smoke.” then:
Unless “otherwise” = the opposite of “You can smoke”