Christmas decorations can be setup almost anywhere there is space. Here near a public park and next to a taxi base, trees and Poinsettia plants (which are native to Mexico) are sold starting 6 weeks before Christmas Day
Various "Nativity" Sets made from dyed and dried corn husks. Some with ornamental decorations. Each small set sells for about $10 USD.
Ornamentary my dear Watson
Hand blown glass ornaments sold in a store in San Angel (Artist's Market)
Saint's candles in a Catholic church. Each candle represents a different prayer topic that people may light.
Stairs to a restaurant's upper level near the Zocalo in Mexico City