How can I disable the notifications prompt in Safari?
Since the release of Safari 7.0.3 Apple finally gives us an option to turn off safari notification prompts. To disable safari notifications go to Preferences within Safari. Click the Websites tab (notifications tab for older versions of safari) and uncheck "Allow websites to ask for permission to send push notifications". And voilà.

Websites panel for current Safari (as of High Sierra):



Panel for older versions of Safari:



The explanation below is only valid for versions of Safari before 7.0.3

Apple obviously forgot the option to disable the notification thing in Safari altogether when they added the feature. Anyway this works, but is not for the faint of heart. ** This is only for older Safari before Version 7.0.3 **


Stop Safari
Open Terminal
cd ~/Library/Safari
chmod 000 RemoteNotifications/


That's it. 
The chmod 000 just makes the directory RemoteNotifications inaccessible. To make it accessible again (and to re-enable notifications in Safari) just do the above again but use 755 instead of 000 in the chmod command.

As lined out in Renés comment below, it is also possible to change the access rights via Finder.