The ordinary doweled joint, by which the post takes the rail, is still used for nearly everything. It is a very satisfying method of working and it is a fine thing to see, for example a set of rails and posts with hole, peg and groove. Once the piece of furniture has been put together, however, no more is to be seen of this often very expensive jointing. This jointing sometimes gives rise to an unintentional plain surface. It is understandable that people should wish to emphasize this constructional achieved form still more with decoration. The jointing employed here was an obvious choice because of its simplicity and clarity of expression. Moreover, it is particularly strong because the ends of the wood retain their full strength. It requires very little time to produce, which makes it appropriate to modern labor conditions. The greatest advantage is that it gives extreme freedom in the positioning of the rails, which achieve a greater expression of space, enabling one to break away from the constructional tied plane surface. (note 1)

http://www.bamboo.org/abs/BambooOnTheInternet.html 
http://www.kauai.net/bambooweb/bambooslides/boo1-25.htm 
the image by courtesy of the last :-) 

Merrel explains this category of Peirce's signs as follows: 

A Dicent Indexical Legisign is characterized by a commonplace expression... Its fully embodied meaning remains vague, since the sign and its 'semiotic subject' are not yet drawn from the limbo of covert relations. (note 2) 

The meaning of any sign and any set of properties partially specifying it is always open to further  specification either on the part of the utterer by way of her engendering successive thought signs or the addressee through his ongoing interpretation of them. (note 3) 

As an index its fulfills the function of a representamen by virtue of a character which it could not have if its object did not exist, but which it will continue to have just the same whether it be interpreted as a representamen or not *(CP5.37) 

As a Legisign it contains a general type, 'Legi' implies a repeated use or replication, which becomes, by habit, a general type. (note 4) 

Effectively we are zooming in on the Rietveld Red and Blue Chair evidencing the detail of the joint, or the general type of connection used  not only in this chair but in some other Rietveld furniture as well. The importance of the detail, the fragment, in design products can not be over stressed. It is simultaneously the locus of materialization of concepts or idea's and of manifestation of specialized signification. Nothing extraordinary if we limit our consideration to the expression of function, for example the connection function of joints, but if we pay attention to other types of signification, such as the hidden meaning of form, texture and color, we have a different picture. What is the meaning of convexity versus that of concavity, or of flatness ?  Ribs and holes, glossy surfaces, transparency, color: all these are enigma's to solve. 

Even characters simulating functionality often serve to convey hidden messages, such as efficiency, modernity or sportyness. The catalogue of these signs is virtually endless, its use fundamental to the appreciation of the design product as designers and marketing know. The reason for this capacity of penetration in the mind of the users is however less known. My explanation is that they may escape partly from pragmatic explanation, exposing merely a modest subordinate detail of the whole product, the global product being instead mostly an explicit  expression of its potential general function, such as: apt to sit upon, to look at a screen, to travel in, etc. In this subtle way those Dicent Indexical Legisigns inherent to details continue to feed our subconscious Jungian archetypes 
 

In the Cabbalah, this sign corresponds to Hesed or Chesed, the place of Mercy and Receptive Intelligence: it is also the topos of forces that actually cohere into forms. 
 

Hesed is the supreme height of manifestation of form: it emanates all rulership over the world of forms; it is called the sphere of the masters; 
Hesed which is he first of the form Sephirah proper and receives the pure abstract spiritual forces from the Supernals. (note 5)