Collectible M & M's TrainsKeep your M&M collection on track with M&M trains. Some M&M trains come in the form of ornaments, and only make an appearance once a year while other figures are on display year round. The variety of M&M keepsakes the feature a train theme include candy toppers or stand alone figures. Trains are an enduring popular theme that enjoys tremendous popularity with kids as well as grownups who are still kids at heart. The combination of the train theme with animated M&M characters makes these pieces especially appealing. In spite of their widespread popularity, it's still pretty easy to find M&M trains online selling at very affordable prices.