What are the tell-tale signs or symptoms of eye cancer?

Depends. Eye cancers include lesions on the lids which can cause focal redness, swelling and pain; lesions on the conjunctiva which lead to redness and irritation; iris cancers which can cause vision loss and iris distortion and choroidal cancers which include melanoma causing disturbance of vision or metastatic also disturbing vision. There are other rarers cancers as well. Consult your ophthalmologist.