Cras Es Noster
means "Tomorrow YOU are ours"
Cras is only an adverb
Es means "you are" - nothing else.
If you see this on seals etc. it is intentionally mistranslated to hide its true meaning.
To say "The future is ours," or "tomorrow is ours," you can say "crastinum est noster." [est with a t]. It is more logical and grammatical to say "crastinum erit noster," 'the future [tomorrow] will be ours.'