The reigning F1 world champion was among the leading critics of the halo proposal tested by Ferrari during the winter.
He is also unimpressed with the screen that Red Bull will trial on Daniel Ricciardo's car in Russian Grand Prix practice on Friday.
"If they're going to do this, close the cockpit like a fighter jet," Hamilton said.
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"Don't half-arse it. Go one way or the other.
"That screen looks so bad. It looks like a bloody riot shield.
"You've got this cool, elegant futuristic Formula 1 car, and you've got a riot shield sitting on top of it.
"And the other one [halo], the carbon fibre structure was obviously good but Fernando [Alonso] wouldn't have been able to get out of the car potentially in his crash in Melbourne.
"But on top of that, it is a good thing to see the FIA does take safety seriously.
"It is a constant thing that always needs to be worked on - as long as it doesn't affect the aesthetics, the style and the coolness of Formula 1."
Although the FIA has made clear it wants some form of cockpit protection system in place for 2017, Hamilton admitted he prefers the open cockpit "the way it is".
While praising safety advances as "amazing", he believes an element of danger is key to F1's appeal.
"When I get in that car, I know that there is a danger," said Hamilton.
"That's been the same since I started when I was eight years old.
"That's a risk that I am willing to take and that every single driver that's ever got in the car has been willing to take.
"You look at Formula 1 as a kid and think 'these guys, they're crazy, they could die at any moment...'
"Everyone comes to me who's just started watching Formula 1 and says 'oh it's so dangerous'.
"That's a large part of why they are so in awe of what you do.
"Take away all that and that person could do it, almost."
Force India driver Nico Hulkenberg was also among the leading opponents of the halo.
He admitted he now sees little point in objecting to cockpit protection systems if one is inevitable, and would favour the aeroscreen.
"From the renders I have seen on the internet it looks better, more attractive for my tastes," said Hulkenberg, speaking before Red Bull's design was displayed in the pits for the first time.
"I think it's unavoidable that it comes so that [the aeroscreen] would be my preferred option."
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