They appear the first time you travel through a Mass Relay - a soulmate tattoo. This unique little marking, somewhere on your body, that will tie you to your true partner with an identical tattoo. If you can find them.

An injury causes Shepard to lose her ability to create new memories, with devastating effects on the events of ME3. How can the galaxy overcome its greatest threat without its hero? Is there anything they can do to mend the past or better the future? FemShep/Garrus.