The "Bleibtreustrasse" that Bloom sees listed as an address in an ad is an actual street in the Charlottenburg district of Berlin, named after the painter Georg Bleibtreu in 1897. But its English equivalent would be something like "Stay True Street," or "Remain Faithful Road." When Bloom thinks in the next moment, "Nothing doing. Still an idea behind it," he is referring to the Agendath Netaim proposal, and the idea is Zionism. But Bleibtreustrasse implies a second kind of idea.

John Hunt 2017

The Bleibtreustraße on a 1900 photo postcard. Source: Wikipedia.