You do not have to sign it. Just before you submit your application, you will be asked to sign (print your name) and confirm the whole application package.
This is wrong info. Please do not suggest something that you are not sure of. CIC specifically have asked not to print it and sign and then upload. Please refer the below link form CIC
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=740&top=23
Here is the text from the above link (verbatim)
How do I sign my online visa application?
You will have to type in your name and answer a security question to submit your application. This is your electronic signature.
Do not print out your application form to sign it.
Do not use the “signature panel” at the top of the screen
To sign your online application:
1) Type your name in the box provided.
Your given name and last name must be exactly the same as on your application form. For children under the age of 18, your parent or guardian must electronically sign your application form.
2) Answer the security question.
The security question is one of the four security questions you created when you registered for your MyCIC account. You must answer exactly as you did when you enrolled in MyCIC.