Link commits from submodule to the parent repository

I have the following situation:

– parent repo (here I write my issues)
— submodule repo1
---- server app
— submodule repo2
---- client app

My question is can I link commits from sub1 and sub2 to issues created in parent repo?

Yes, just use the <user>/<repository>#<issuenumber> notation, which works across any GitHub repository. Issues thus mentioned in commits messages will show a link to the mentioning commit in their thread.