If you have a strong theory about how silicon based life might arise then of course you could look for signs of that. What are those signs? Well, ... that depen

If you have a strong theory about how silicon based life might arise then of course you could look for signs of that. What are those signs? Well, ... that depends on your theory. Versus carbon based water dependent life? We know it exists in at least one form and what its characteristics are. So we have plenty of candidates for "signs of life" in that form. It doesn't mean it's the only or even best way to search, it just means it's the one we know how to begin! Edit: You might also enjoy reading about this semi-related topic: https://en.m.wikipedia.org/wiki/Anthropic_principle https://en.m.wikipedia.org/wiki/Anthropic_principle