It is a sandwich/cake shop selling wonderful slices of pizza. If you are staying at Porta San Mamolo hotel and arrive in between meal times (which appear to be fairly rigid in Italy!) go round the corner and experience very delicious sandwiches & pizza (which they will warm up for you).
From Hotel Porta san Mamolo it is 1 minute walk. From hotel door turn right, at the end of the street turn left along Via Paglietta and then right and it is on the corner of Viale Enrico P and Via Massimo.
The display of sandwiches is priceless. It typifies the sheer quality of food in Bologna. You can see lots of other places to eat there at www.tasteforbologna.blogspot.com