Franco claims West Ham deal
"Imagine how I feel after so much criticism for not having a team but thank God my dream has come true to play in England," Franco told reporters.
"This is a new step, a new cycle with big challenges in a very strong league," the former Villarreal player added.
West Ham, 11th in the table with four points from three matches, have yet to announce the 32-year-old former San Lorenzo and Monterrey forward will be playing for them this season.
Argentine-born Franco's contract with Spanish club Villarreal expired last month and a move to South American champions Estudiantes in the country of his birth fell through due to late registration.
A member of Mexico's 2006 World Cup squad in Germany, Franco was called up by national team coach Javier Aguirre for this month's 2010 qualifiers despite having no club and scored in the 3-0 win away to Costa Rica on Saturday.