Hide post titles selectively

Hello,
while blogging on my personal blog I don’t always use post titles. Thus, I’d like to add to my theme a structure like this (pseudocode):

if
post_title != "no title"
than
display post_title

Anyone can help?
Thank you

PS: I know I could just add a custom field (as suggested here), but I’ve just imported hundreds of post from a previous blog and the whole operation would be a bit tedious.