They're called "wire-loop" style snow guards. They were the most common style in the late 19th - early 20th century. They're not as common as the other styles now, but they're not unusual. They're still manufactured. There's a formula based on pitch, but there should be a minimum of 50 per square. The guards in your pics are all bent. From my 1899 A Treatise On Architecture And Building Construction Volume 3: "Should this form of guard be bent down by the weight of snow and ice, it may be readily pressed back, without breaking, into its proper position. Guards are also manufactured of cast iron, but, being clumsy, they are not to be recommended".