From Istanbul Turkey to Bukittinggi Indonesia, muslim civilization shares many things in common. One of them is the mosque architecture. Majority of the mosque in middle east and south east asia have hemispherical dome and tall circular or polygonal shaft minaret. The copper or aluminium finial is usually ornamented the top of the dome and minaret.
Certainly there are more artistic designs and very long lasting materials than simply metal based finial but what we are seeing in this picture are example of ordinary metal ones. The street shop is run by an old man and specially selling mosque finial and nothing else. As pictured there, the showroom has two design of zinc or aluminium finials only and I believe they are suitable for small mosque (mushalla). Why two ? let you guess, maybe the local handcrafts men only brings "standard" design each year or maybe those are the most sellable ones :-) For information, this shop is just opposite of Masjid Agung near Janjang 40 Bukittinggi central.
p.s Compared with the copper finials found in the antique or tourist shop in Istanbul (c Andrea Kirkby photo).