By way of background, Resin Identification Codes (RIC) were originally developed by the Society of the Plastics Industry (SPI) in 1988 to identify the plastic resin used in manufactured articles. The codes originally consisted of a number inside a triangle formed by “chasing arrows.” The numbers signified the type of plastic used in the product. SPI began to work with ASTM International in 2008, and in 2010, ASTM D7611/D7611M - 18, “Standard Practice for Coding Plastic Manufactured Articles for Resin Identification,” was issued. D7611 was revised in 2013. One of the revisions was, as you mentioned, a change from the “chasing arrows” symbol to a solid equilateral triangle around the numbers.  This was done to eliminate any confusion between the resin codes and the universal recycling symbol of chasing arrows.

Concerning your first question, there are no U.S. federal regulations requiring the use of ASTM D7611; however, at least 39 states have enacted legislation on the use of these codes.

You also asked about the continued use of the “chasing arrows.” ASTM explains in the scope of the standard (see link above), “It is possible that some states or countries will have incorporated the original SPI practice into statute or regulation. In those situations, that statute or regulation takes precedence over this standard.” For example, California law (Public Resources Code section 18000 et seq) requires that rigid plastic containers sold in California be labeled with a code to identify the resin used. The law further specifies that the code “shall consist of a number placed inside a triangle, and letters placed below the triangle” and that the triangle shall be formed by three arrows.

Generally speaking, products imported into a state with resin identification regulations need to comply with the regulations of the state of import absent exigent circumstances.