Numerous observations: Black Lives Matter is a violent marxist organization, and looking at the context around this sentence, they are clearly voicing support for this organization. The statement itself is not at fault, as black lives really do matter, however, as already stated, in context, this statement is a red flag.

"No human is illegal" is a leftist slogan which states that "illegal immigration" is not distinct from "legal immigration". On the surface, this appears true. However, once you look a little deeper, you immediately realize the glaring problem: criminals are, by definition, illegal. A criminal immigrant (by the laws of the country he wishes to go to) must therefore at least be considered an illegal one, unless he is directly approved by the nation itself. The existence of the state apparatus clouds this issue some, but with the torchlight of logic, it is possible to look past this fog also.

"Love is love" is a slogan of the L+ Lobby. Like the phrase "Black Lives Matter", it is a true statement on its own (as a simple assertion that whether a person is homosexual, heterosexual, or bisexual, their feelings are their own, and their bedroom is their own), but in context, this is a statement of support for a lobby that tries to systematically demolish the freedom of association human beings have.

"Women's Rights are Human Rights": This is true, but it makes no sense to put this on a yard sign, as there is no objective measure by which women lack legal rights that men have. Social rights may differ, like for example, women lack the social right to be persecuted for rape and false rape allegations, which is a right men have in abundance. However, social rights are not lobbied for like this, they require precise, sharp argumentation in a civil-discourse setting.

"Science is Real" is not true. Science cannot be real, as it is a construct of the human mind. Science is meant to aid us in our understanding of the world, not be a blind faith. Scientists should want to be doubted so that they ca absolutely BTFO the unscientific doubters with nothing more than facts, or admit defeat and reqork their systems like absolute chads, but instead, hedonistic Statist culture (although the two are inseparable) has turned pop-science into science worship

"Water is Life" is not true. Hydration is necessary for human beings as they exist today, but there are many organisms which do not require water, and there is such a thing as overhydration, and deaths thereby, though it is much rarer than its counterpart, dehydration. In response to OP, I have a few more things to say:

Global warming, as a narrative, is false, but the keeper of the yard sign would likely believe in it, considering their sign contains "Science is Real", which is a common alarmist/Malthusian propaganda phrase, which means they likely unquestioningly trust whatever bowtie-man says on TV because he has a Ph.D. (yet another reason Rothbard should be required reading; bowtie man with several Ph.D.s spitting facts right there) however, it is undeniable that the world is getting warmer. this is simply not reason to be alarmed as: it is a natural process, which humans will survive.

This means alarmists most of all, believe rising sea levels will make this world an ocean planet by last week. However, you cannot then take the statement "Water is life" and say "Then isn't global warming a good thing?" As it is not an argument. The keeper of the sign obviously does not mean to say that all water is good and that there exists no such thing as "Too much water", and in fact, the intended meaning here is not a discussion- you also think water is necessary for survival. Claiming that saying "water is life" means you must like floods, then, is not civil discourse, it is nitpicking terms. You know damn well what he meant and you don't need him to be clearer.