Sign ups for a beta launch. What are good indicators?

I have been working on a startup for some time now, and a couple of weeks ago we came up with an idea for a pivot (the original startup isn't getting the traction we were expecting).
To avoid the same issues as with the first one, we decided to follow a different strategy, mainly based on this:

http://blog.kissmetrics.com/do-these-4-things/ So, we have used launchrock to create a landing page (we are using a different name for this pivot), with some screenshots of our mobile app and a list of the features, asking people to sign up to get a notification when the app is launched. Then we are submitting our startup in as many sites as we can, and are trying to engage users that could be interested in our app throught Twitter and Facebook.

It's been a week since we launched the landing page and so far, according to Google Analytics, we have had 120 unique visits, with 15 people signing up on the page (we ask only for the email).

Now my question is, how do I know if this is a good number or not? How can I tell if people went to my site and found out they don't like my idea or if it's just that people are not so eager to give away their emails?
Has any of you done something similar in the past? what's a "normal" conversion rate? What other strategies would you suggest?

Thanks a lot for your time

You have a sign up rate of over 10%, first thing to emphasis from cold (i.e these are not people you interacted with previously) that is impressive but unfortunately probably skewed by your friends and while it might sound scary there isn't really enough visits or signups to identify any trends of patterns statistically with any sort of reliability.

It's also worth baring in mind that signups on your mailing list while a great start do not convert to instant sales. Many sales teams refer to leads on a scale of cold to hot, someone coming to your site for the first time is just above freezing, someone signing up to be notified is still lukewarm.

Personally if it was me, I would add first name to the sign up form, or some mechanism to personalise the emails you will be following up with. I would also start to get build a relationship with my signups, with regular email contact, maybe send out a survey to garner feedback etc. In such a scenario I would expect to see a reasonably high unsubscribe rate but that's ok, you can repick those people up when you go live.

For the list to be useful you need to grow it someone asked how to gather beta users a few days and their were several people chiming in with ideas which might be worth reading.

In terms of working out success, first you need to define what your goal is?
I would suggest signups while a short term goal are almost irrelevant compared to sales/downloads. When you launch the idea is your email list provides a little push an maybe a means to spread the launch rather then be the single source of sales. Where a list can be very useful is validating ideas, is your list willing to pay for your idea?

It wouldn't hurt on your signup page add a short survey, that doesn't require an email to answer, which has one line text boxes for the answers to your questions:

• What do you think of my idea?
• Do you know of anything else done like this?
• Are you leery about signing up because I'm asking for your email?

Also, under your sign up form, make sure you explicitly state that you will NOT ever spam them and will never give their email address away to anyone. You will only use their email to let them know about progress with your product.