apk vs signetd apk code example

Example: difference between signed apk and unsigned apk

Signing Android apps is just like signing any other application;

it provides the user with some level of assurance that the code hasn't
been tampered with since you released it.

Unsigned apps should be usable generally but do require lowering the
security level. A quick Google search found a number of articles that
explained that all you have to do is check the Unknown Sources box in
Settings->Security.