Sign Instance
GET /data/api/signs/220/?format=api
http://labasi.acdh.oeaw.ac.at/data/api/signs/220/?format=api", "sign_name": "APIN", "abz_number": "56", "meszl_number": "90", "image_1": "http://labasi.acdh.oeaw.ac.at/media/sign_img/apin_56.jpg", "image_2": null }{ "url": "