Sign Instance
GET /data/api/signs/135/?format=api
http://labasi.acdh.oeaw.ac.at/data/api/signs/135/?format=api", "sign_name": "ŠU", "abz_number": "354", "meszl_number": "567", "image_1": "http://labasi.acdh.oeaw.ac.at/media/sign_img/sign_354.bmp", "image_2": null }{ "url": "