Apparatuses for providing a visual indication outside a blowout preventer (BOP) relative to a position of ram blocks inside the BOP, and methods of adding such apparatuses to existing blowout preventers are provided. An apparatus has an indicator rod, a detectable portion and a sealing assembly. The indicator rod has an end extending outside an end cap of the BOP, and is configured to engage with a tail rod of a ram block of the BOP, and to switch between a first position when the BOP is in a close state, and a second position when the BOP is in an open state. The detectable portion is located outside the end cap and is configured to provide a visual indication relative to a current position of the indicator rod. The sealing assembly is configured to seal a space inside the end cap from an environment in which the BOP operates.