Unity function to get all properties in a SerializedObject with an attribute.

GetPropertiesWithAttribute.cs

// Example usage inside Editor.OnSceneGUI for Vector3 fields:
//
// foreach (var property in GetPropertiesWithAttribute<MyCustomAttribute>(serializedObject))
// {
//     Handles.Label(property.vector3Value, property.name);
// }

static IEnumerable<SerializedProperty> GetPropertiesWithAttribute<TAttribute>(SerializedObject serializedObject)
{
    var targetObjectType = serializedObject.targetObject.GetType();
    var property = serializedObject.GetIterator();

    while (property.Next(true))
    {
        var field = targetObjectType.GetField(property.name);

        if (field != null && Attribute.IsDefined(field, typeof(TAttribute)))
        {
            yield return property.Copy();
        }
    }
}