There is an underlying connection between classical Persian poetry and religion. Although religion can be considered as one of the main origins of the poetry, it seems that in the contemporary poetry this connection has become partly weak. Here, we aim to study the religious signs of Forough Farrokhzad’ s poetry, one of the Iranian modern poets. To do so, we initially introduce and discuss Peirce's Theory of Signs. Then, according to this theory, we start to analyze her poems. This aspect of her poetry has not been discussed that much until now. There are plenty of religious signs in Forough Farrokhzad’ s poetry. She uses both Islamic and Christian elements, but the way she chooses the signs and the way she uses them, both are completely different in line with each religion. At the beginning phases of her poetry, the religious signs, which are mainly Islamic, enter into her poems through the classical literary works and therefore they are mostly abstract. But as her poetry grows more mature, she changes the way she applies them. In this phase, the frequency of Christian signs, picked up from Gospel, increases in her poetry. On the other hand, at the same time, the Islamic signs of Forough’ s poetry are picked up from the environment in which she lives, instead of the foresaid classic works. So, as a result, these signs are objective, tangible and related to the folk religion.