There should be a small mark near the task if there is smth inside it’s “details”.
Welcome to the Community Forum @Elbruz_Keskin!
Thanks for sharing this feedback! It’ll be very helpful if you can give us more details about your request. For example, would you like to see the mark when the task has a description? or do you feel it would be a good idea to include in the project list view? 
It will be good to see which tasks have description.