Yes it's legal to take them down. Anything put up by ordinary citizens like that can be taken down as well. Only things put up by the city or with special permits are prohibited to remove or damage.

Who told you they had razor blades behind them? There's some odd pernicious myth, usually about fascist posters that they put razors behind them yet there's little evidence it was ever a widespread thing (among other things it turns something cities ignore into a potential crime).

I would suggest a knife to cut 2-3 pieces of tape then just tear them off to do so quickly. The thing to watch out for is there may be little loyal zionists watching who might try and take your picture and try and claim hate crimes or whatever, best not to be photographed anyways as they'll slander you. I once took down some Falun Gong posters and some lady appeared out of nowhere and tried to take my picture but she was too far away and I just turned and ran off before she could get closer lol.

Beware that one of the main purposes of these posters is to generate outrage and demonize supporters of Palestine when they are taken down. Consider putting up your own posters over them, ideally glued to the entire thing so they have to take down their own poster in the process if they want to take down yours. Here are some options:

In my country they've actually posted giant versions of these ads on street boards.

Wear a face/eyes covering (e.g. mask and goggles), long black clothes that cover any body identifiers (e.g. tattoos), and perhaps some Kevlar gloves if you are paranoid. Ideally cycle to the location to & from a discreet clothes-changing station. The main threat here is doxxing and not legal-related.

I would approach this with the same caution that the Black Bloc approaches protests, especially since the "safety in numbers" is less of a factor here. Although if you are willing to accept some social risk, feel free to drop some of the more prohibitive precautions.

Legal yes, but probably not very ideal if you're caught on camera doing it

If you have to drive, to your mission POI, park near where the posters, but not directly next to them. Have a an obfuscated place like the back of a building where the trash is that you can change into unusual clothes. Wear clothes that are atypical of your identity over your normal street-wear and a covid face mask to conceal your face. Sunglasses can also obfuscate your face. Your unusual clothes should best not stand out. If someone photographs you, they are unlikely to identify you. Facial recognition software i heard can't identify people in covid masks very well. You can also wear an atypical hat. After you remove the posters, go to on foot the place that is obfuscated like a trash can to change back into your normal street wear if not followed. Make sure that you do something that your public identity would do nearby where you car is parked.

Signage laws tend to be at a local/city level rather than state or federal.

So it basically depends where you are (please don't dox yourself) what the rules would be.