Is it obligatory to inform the person that the money given to them is Zakat, or is the intention sufficient?

It is not obligatory to inform the recipient of zakat that what he is receiving is zakat; only the intention of the giver (muzakki) is required. Some scholars disliked informing the poor that the payment is zakat so as not to embarrass them. Ibn Qudamah narrated from Imam Ahmad, who said: "He gives it to him and remains silent; what need is there to make him feel ashamed?" Displaying zakat is better than concealing it because it is one of the great شعائر (rituals/symbols) of Islam, and in displaying it there is benefit and welfare for society. This is unlike voluntary charity (sadaqat al-tatawwu'), where concealment is preferred to avoid ostentation (riya').