Another +1 for Subsurface. You can log all of the information you want in the various sections such as buddy,, DM, suit, weighting (including how the weight was used such as belt, harness etc) location (including GPS if you have it), photos and videos. All of which comes in handy later when you want to remember which dives you did with a particular buddy or how much weight you needed with a specific suit.
Also with having cloud storage, it allows you two sync multiple devices such as desktop, tablet, PC, MAC. I use my phone to sync from the Perdix which then syncs with the cloud and I can add further details later (end of the day or end of the trip)
As for signing, apart from doing certain courses (which are dive number limited such as DM, instructor, solo etc), you will find that almost no-one needs or wants to see your log apart from you. Even with those they won't need them signed.