Skype is catching up with pretty much every other chat program on the planet by finally adding read receipts. When someone has seen your message, their avatar will pop up below, so you can see at a glance how up to date they are with your conversation.
The feature is available in one-on-one conversations as well as group chats with as many as 20 people; everyone will need to use the 8.26.76 preview build on iOS, Android or desktop for it to work. If sending read receipts is not your jam, you can turn them off in your privacy settings and they are disabled in any case
Another example of Microsoft playing catchup at least they can say they have the functionality now good job on their part. With the addition of secure messaging this was a must.