"Bleibtreustrasse" 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.
The ad for the agricultural investment promises "Your name entered for life as owner in the book of the union"—quasi-legal language for investment in a real estate partnership, but also a fair description of a successful marriage. It seems possible that Joyce may also be making teasing references to Bloom's domestic situation with the numbers that he attaches to the street. The postal zone code, "15," is Milly's age as of yesterday. The address on Bleibtreustrasse, "34," does not line up with Molly's age quite so neatly. She is 33 on June 16, and will not be 34 until September 8. However, given the deep uncertainty that Molly expresses about her own age in Penelope—"the 4 years more I have of life up to 35 no Im what am I at all Ill be 33 in September will I"—perhaps some kind of allusion to her age can be heard in the number.
Collectively, these details impart a symbolic function to the Agendath Netaim advertisement. The allure of participating in the Jews' return to their spiritual homeland bleeds over into Bloom's desire to maintain the home that he has made with Molly and Milly, a domestic stability that is threatened by Molly's adultery and Bloom's epistolary infidelity. Similar symbolic overtones will attach to the two songs that Molly plans to sing on her concert tour—Là ci darem and Love's Old Sweet Song—and to the story that Bloom reads from Titbits.