Hi E.,
LOL, well I can tell you some of the clues in my own behavior/thoughts before I had my first...(my husband and I were married 7 years before choosing to get pregnant, by the way).
I used to look at babies and other folks' kids and think "aww, aren't they cute" and would even play with them for a bit, but only a little while and I never really had any deep desire to have my own. The first change I noticed in myself when I was ready is that I started looking at babies/kids, or playing with them or caring for them briefly and thought "I could just take you home with me!" ...and I meant it! I could actually picture myself with a child in my own arms, my own home, taking care of him or her (yes, even through the stinky and noisy and frustrating bits!). That was such a stark change from how I had felt before that it really was a signal for me.
Aside from that, I began looking at the things I did as fun and productive and good, but began realizing that I really was willing to cut back on those things and even put some things aside to have and care for children. Mind you, I also have an extremely good husband who helps with housework, cooking, etc., and who is very loving and even-tempered, so I knew I would not be doing everything alone (at least not all the stinky, noisy, frustrating bits alone, hehe).
That's about all the help I can offer. I will say that even with those clues, and feeling I was ready, it was *still* a huge adjustment once the baby came. They are a lot of work, and I have had to change my life a great deal, but honestly I can't say there's anything I've had to totally give up - except for my beadwork...that's a little too hard to keep contained with a small child around the house. But even that I've just packed away for when my daughter and the baby that's on the way gets bigger.
We don't travel as much, of course, but we had done a good bit of travelling before, and we can do it again after the kids are grown, so I'm not really missing that too much. As a matter of fact, I'm rather enjoying having a household and being settled. It's where I'm supposed to be right now.
I'm not saying I don't have moments where I get frustrated, a bit stir-crazy, or feel like I need to just get out of Dodge (who doesn't!). Sometimes I do miss my child-free life, but those times are infrequent, and my daughter's kiss or hug or giggle makes me remember why I chose to have children. And my husband and I make sure that we each have time to ourselves at least once a week. Every now and again one or the other of us even takes a weekend off and goes to a workshop (for me it's dance) or to visit friends out of town. It's important that you have a partner that works with you and that you help each other when one or the other is getting burnt out.
If you have that, then you're ready I think. Everyone is different though. I can't say what your clues will be, I can only share what it's like for me.
Good Luck!
J.