It is considered good luck for a chimney sweep to attend a wedding.
In Dickensian England, chimneysweeps were often young children in that they were small enough to climb up chimneys. The job was filthy and dangerous with the children often being mistreated.
Nonetheless it is considered good luck for a chimneysweep to attend a wedding and kiss the bride.
About 200 years ago in England a chimneysweep supposedly saved the life of King George 11 by stopping the runaway horses of the royal carriage. In gratitude, King George decreed that all chimney sweeps were lucky. This developed into a custom and belief that it was good luck for a marriage for a chimney sweep to attend the wedding to shake hands with the groom and be kissed by the bride. Since that date all royal marriages have had a chimneysweep in attendance and it has been common in England to hire a chimneysweep to attend weddings. The custom spread to Australia and some weddings still follow the custom. There are various firms that offer the services of a chimneysweep to attend weddings.
Since the late 18th century sweeps have been considered good luck in a general sense as well. On seeing a sweep in the street in his working clothes and with his face blackened, one had to bow, raise one's hat, curtsey, or call out a greeting, such belief being especially true amongst coachmen and race-goers. It was also considered to bring good luck to shake hands with a sweep or to blow him a kiss. These beliefs and customs predate the King George decree.
Chim chim cher-ee!
A sweep is as lucky
As lucky can be
Chim chim cher-oo!
Good luck will rub off when
I shake 'ands with you
Or blow me a kiss
And that's lucky too
Btw, P L Travers, the author of the Mary Poppins books, lived in Ashfield NSW during her later school years. There is a statue of Mary Poppins in Ashfield Park: