Likely the buildings' names. Almost all of them seem to be named "Dream Residence [number]".

https://web.archive.org/web/20230605093451im_/https://dream-residence.com/themes/azur/img/dream-residence-map-opt.jpg

Note that their site (dream-residence.com) now redirects to https://greendistrict.bg which might be this project, or it might be a new project.