Giving someone a clock means to symbolize the passage of time, appreciation for the recipient's time and presence in your life as well as thoughtfulness.
Giving someone a watch can also symbolize these things.
And in some cultures giving someone a clock or a watch can also mean and is considered a faux pas, particularly in Chinese culture, where it's also associated with attending a funeral.
A clock is a constant reminder of the passing time and encourages the recipient of the clock to value each moment.
The clock when given to someone can also be a thoughtful gesture, especially when it's personalized with engravings or is chosen for it's quality as well as craftsmanship.
The clock can also signify that you value the recipient's time and appreciate their presence in your life.
Giving someone a clock is also a great way to commemorate special events like anniversaries, graduations or retirements.
And in some contexts, a clock can also represent luxury and the desire for the gift to last.
And in Chinese culture, giving someone a clock is actually considered back luck and is also associated with attending a funeral because the pronunciation of "giving a clock" is similar to attend a funeral.
The taboo also extends to watches as well, though smaller items like wristwatches may be more acceptable.
And although it's not as widespread as the Chinese taboo, some other cultures also have superstitions about gifting of clocks, so it's always best to be mindful of the recipient's cultural background when giving them a clock or watch.