A Colorado Notice of Intent to Lien does not need to be notarized in order to be valid. However, if you end up actually filing a lien claim, you will need to submit an affidavit affirming that the Notice of Intent requirements were met, which does need to be notarized; as well as the lien claim itself.
Here are some additional resources you may find helpful:
You can download a free Colorado Notice of Intent form here. The template also includes the Affidavit of Mailing and a Statement of Lien form as well. Good luck!