I wonder if you are looking for the ceramics artist Lisa L., or Lisa Larsson, who signed her work Lisa L, or Lisa Larsson for Gustavsberg, which is in Sweden.  There are many of these colorful plaques for sale by this artist.  Here is just one example of her work, and if this is the kind of tile that you have, perhaps you could contact this person to learn more about the artist, her work and what the tile might be worth. http://www.trocadero.com/stores/serendib/items/633117/item633117.html  Here is one more site that sold a ceramic tile by Lisa Larsson, and this person also may be able to give you the information that you require: http://www.pips-trip.co.uk/sold-items/sold-ceramics-1/showitem-GUSTAV-LISAL1.aspx.