It seems an unlikely symbol to find in jewellery but it has been used. Like the shield, it implies protection from harm. It was, of course, a symbol of knighthood and chivalry. There are also aspects of balance needed to make a sword. Daggers are traditionally associated with honour.
This first photo shows part of an amazing silver collar I bought recently. This collar is associated with the Portuguese Royal Military Order of the Tower and Sword which was created in 1459 by King Alfonso V. The Order was revived in 1808 to commemorate the arrival of the Portuguese Royal Family in Brazil after Napoleon invaded Portugal. It survived being abolished by the Republican Government in 1910 when other military orders were, and still exists today. You can see that the collar contains alternate tower and sword links.
The Victorian brooch at the top of the post is a fairly common example of such pieces, usually from the latter part of the era. This one has a crescent moon set with seed pearls in the middle of the brooch with a small garnet star in the middle of the crescent. Pearls have long been associated with the moon, not only because of the creamy white colour but because they come from the sea, which is ruled by the moon and the tides. The sword handle is also set with seed pearls. I am not sure of the symbolism around mixing a sword with a crescent moon.
The last piece is a Scottish dagger or dirk brooch set with various pieces of agate and with a cairngorm gem on the top of the hilt. You can see that it also has two little dirks tucked down its length. Queen Victoria and her family started to spend their summer holidays in Scotland and in 1847, she purchased Balmoral Castle to serve as her holiday house. One of her interests was the jewellery made in Scotland using local ornamental stones. This jewellery was described as Scottish agate or pebble jewellery and it became very popular. Initially, the jewellery took the form of practical items such as kilt pins and plaid brooches but expanded into every form of jewellery, such as silver bracelets, complete with buckles and inset with agate, heart clasps, belt clasps, anchor brooches, earrings and charms.