English verb conjugation
CAN SIGN

Regular verb: sign - signed - signed

Affirmation

Simple form	V-ing form
I can sign you can sign he can sign we can sign you can sign they can sign	I can be signing you can be signing he can be signing we can be signing you can be signing they can be signing
Perfect	V-ing perfect
I can have signed you can have signed he can have signed we can have signed you can have signed they can have signed	I can have been signing you can have been signing he can have been signing we can have been signing you can have been signing they can have been signing

Negation

Simple form	V-ing form
I can't sign you can't sign he can't sign we can't sign you can't sign they can't sign	I can't be signing you can't be signing he can't be signing we can't be signing you can't be signing they can't be signing
Perfect	V-ing perfect
I can't have signed you can't have signed he can't have signed we can't have signed you can't have signed they can't have signed	I can't have been signing you can't have been signing he can't have been signing we can't have been signing you can't have been signing they can't have been signing

Interrogative form

Simple form	V-ing form
can I sign? can you sign? can he sign? can we sign? can you sign? can they sign?	can I be signing? can you be signing? can he be signing? can we be signing? can you be signing? can they be signing?
Perfect	V-ing perfect
can I have signed? can you have signed? can he have signed? can we have signed? can you have signed? can they have signed?	can I have been signing? can you have been signing? can he have been signing? can we have been signing? can you have been signing? can they have been signing?

Interro-negative form

Simple form	V-ing form
can't I sign? can't you sign? can't he sign? can't we sign? can't you sign? can't they sign?	can't I be signing? can't you be signing? can't he be signing? can't we be signing? can't you be signing? can't they be signing?
Perfect	V-ing perfect
can't I have signed? can't you have signed? can't he have signed? can't we have signed? can't you have signed? can't they have signed?	can't I have been signing? can't you have been signing? can't he have been signing? can't we have been signing? can't you have been signing? can't they have been signing?