From Grade 1 up, it's very important to make sure that students switch to your class in Seesaw before posting, they can check this by tapping on their name in the top left corner, then tapping on the name of the class they wish to switch to. Then, before they leave your lesson, you should remind them to switch back to their homeroom class.
If you don't do this your students are likely to lose work because they are posting it to the wrong teacher.
You never need to ask students to sign out, this causes a lot of work and stress for homeroom teachers!