Hello Nupoet,
Alters sometime communicate with suttle hints, but may also just cause a headache, stomach ache, backache, etc. That is the only way they may know to signal you. They can pass along feelings or dreams. Some may be a playmate that a person has. We are all individuals and so are they, so there is no certain way they communicate. At time they may even communicate with others first. Some can hear you but do not know how to "talk" to you. The host and an alter can learn to think to each other as well as share feelings.