@JoshuaDages It's possible to succeed without a signature style, but it's just SOOOO much harder! Like I said publishers want to see what they're going to get, and especially if you're able to maintain the same style throughout an entire book. What if your main character looks different on every page? Consistency is super important to get professional work. I know it's really hard to pick a style, I for one love to draw in many different styles. And just because you pick one now doesn't mean you have to stick with it for the rest of your life. But you're making it 50 times harder for yourself to start an illustration career if you don't, ans since it's already very hard I don't think you need to do that to yourself... My advice is for now, just pick one and draw 12 pieces in this style, update your portfolio and start sending it around. This is going to make everything so much easier for you!
Also, decide what kind of work you'd like to do and make that kind of work for your portfolio. Want to make children's books? Make book spreads, even if they're fake assignments! That way publishers are seeing exactly what your work would look like as a book. One would think that publishers have more imagination, but sometimes they really don't. If they don't see your work in exactly the right context in your portfolio, they often skip over you entirely.