What is the adjective to describe someone who conspicuosly takes others' things without asking? Can the adjective audacious be used to communicate the idea?
I presume you are asking for an adjective to modify "thief."
"Audacious" means "extremely bold." Whan applied to "thief," it does not entail "visible" or "public." That attribute may be what makes a thief audacious, but climbing down a high wall into a building full of armed guards and watch dogs would also be "audacious."
The word you probably are looking for is "blatant," which describes something done in plain view and without apparent shame.