From Islamic perspective, is it permissible for Muslim women to model (for clothes), become a spokesperson and endorse certain brands? The international brands usually originated from U.S, for example, Avon, Maybelline, Pepsi etc.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Allah enjoins wearing Hijab on Muslim women. Allah says: {…..and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) and not to reveal their adornment except to their husbands, ...} [24:31]
The entire Muslim Ummah has agreed that Hijab is an individual obligation on every Muslim woman. Then how it could be imagined that a Muslimah could be a model, exposing her body for everyone and showing her charm in every gathering! How could it be possible for a Muslim woman to become a trading article in the hands of the industrialists! Whoever indulges in this practice is under the sever punishment of Allah as mentioned in the Hadith that the Prophet (Sallallahu Alaihi wa Sallam) said: ""Two are the types amongst the denizens of Hell, the one possessing whips like the tail of an ox and they flog people with their help. (The second one) the women who would be naked in spite of their being dressed, who are seduced (to wrong paths) and seduce others with their hair high like humps. These women would not get into Paradise and they would not perceive the odour of Paradise, although its fragrance can be perceived from such and such distance (from great distance)" ." This Hadith more likely fits to models.

Allah knows best.