About the 5p:
 
The original reverse of the coin, designed by Christopher Ironside, and used from 1968 to 2008, is a crowned thistle (formally, The Badge of Scotland, a thistle royally crowned), with the numeral "5" below the thistle, and either NEW PENCE (1968–1981) or FIVE PENCE (1982–2008) above the thistle.
To date, three different obverses have been used. In all cases, the inscription is ELIZABETH II D.G.REG.F.D. 2013, where 2013 is replaced by the year of minting. In the original design, both sides of the coin are encircled by dots, a common feature on coins, known as beading.
 
As with all new decimal currency, until 1984 the portrait of Queen Elizabeth II by Arnold Machin appeared on the obverse, in which the Queen wears the 'Girls of Great Britain and Ireland' Tiara.
Between 1985 and 1997, the portrait by Raphael Maklouf was used, in which the Queen wears the George IV State Diadem.
 
On 27 June 1990 a reduced size version of the five pence coin was introduced. The older larger coins were withdrawn on 31 December 1990. The design remained unchanged.
From 1998 to 2015, the portrait by Ian Rank-Broadley was used, again featuring the tiara, with a signature-mark IRB below the portrait.
 
As of June 2015, coins bearing the portrait by Jody Clark have been seen in circulation.
In August 2005 the Royal Mint launched a competition to find new reverse designs for all circulating coins apart from the £2 coin. The winner, announced in April 2008, was Matthew Dent, whose designs were gradually introduced into the circulating British coinage from mid-2008.
 
The designs for the 1p, 2p, 5p, 10p, 20p and 50p coins depict sections of the Royal Shield that form the whole shield when placed together. The shield in its entirety was featured on the now-obsolete round £1 coin. The 5p coin depicts the centre of the Royal shield, showing the meeting point of the four quarters. The coin's obverse remains largely unchanged, but the beading (the ring of dots around the coin's circumference), which no longer features on the coin's reverse, has also been removed from the obverse.  
Credit: https://en.wikipedia.org/wiki/Five_pence_(British_coin)