The crescent symbol is primarily used to represent the Moon, not necessarily in a particular lunar phase. When used to represent a waxing or waning lunar phase, "crescent" or "increscent" refers to the waxing first quarter, while the symbol representing the waning final quarter is called "decrescent".
The Luna, half moon, or sickle of the moon, waning and waxing moon, is a sign of fertility and to the cycles of life and death. It represents the changing of the seasons and the ebb & flow of the tide.
The full moon is considered an appropriate time for all magick related to divination, scrying, protection, releasing, banishing, and overcoming obstacles. It is also the most appropriate time to honor, evoke or invoke lunar deities and Mother Goddesses.
The New Moon (Dark moon), when the moon appears to be completely covered in darkness is a great time for manifesting what you wish to have in your life. It is also a good time for scrying and other methods of divination. Magickal workings aimed at initiating new projects (jobs, ventures, spiritual growth etc...) are also best done within the new moon.
The pentacle is perhaps one of the most recognizable symbols that Wiccans and Pagans use. The base symbol is the five-pointed star, which can be drawn non-stop without lifting pen from paper. Enclosing the pentacle is often a circle. For many Wiccans and Pagans the pentacle is a symbol that represents magic and magical workings as a whole. For others it’s used as a talisman, a connection to the divine, to open and close circles and a myriad of other ritual uses.
*Approximately 5 inches wide & 0.25 inches thick